Almost all modern cars come with some ability to connect a device to play or stream music, but for those with older vehicles it can be a bit more difficult. This is only made worse by the fact that many newer phones don’t feature an audio jack, so plugging in a device to the car’s headset is simply not possible.
If you don’t fancy buying a newer car with Bluetooth connectivity, an easy way to solve this issue is with an FM transmitter. An FM transmitter will let you connect your phone, tablet, etc. to your vehicle’s audio system and play music through it.
In this guide we are looking at five of the best Bluetooth FM transmitters you can buy, and we will be putting them through their paces. We will be covering a range of different areas from ease of use, build quality, connectivity, sound quality and more. Use the table of contents below to skip to the section you are most interested in.
In this review we also cover some of the most common questions and complaints about using FM transmitters to enhance the audio connectivity in your older car.
Table of Contents
What Bluetooth FM Transmitters Will We Be Covering?
IMDEN C57 Bluetooth 5.9 FM Transmitter
Nulaxy KM30 FM Transmitter
Nulaxy KM18 FM Transmitter
Avantree CK310 FM Transmitter
CSYLX BT-X7 Smart Bluetooth FM Transmitter (similar to the LIHAN HY82, YDA BT-X7 and LTS BT-X7)
What Is an FM Transmitter?
An FM transmitter for a car broadcasts a signal (songs, sounds, etc.) from a device such as a phone, tablet, personal computer or an MP3 player to a standard FM radio. Some FM transmitters plugin to a device’s audio jack, but the ones we are looking at in this article are Bluetooth transmitters (although some have the option to play music over USB).
Once the transmitter is connected it can then broadcast a signal over an FM frequency band, so that it can be picked up by a nearby radio (the one in your car in this instance). This means that you can connect newer phones and devices to the audio system of your car, even if the sound system in your vehicle does not feature Bluetooth or any other sort of connectivity with modern devices.
Why Buy a Bluetooth FM Transmitter?
Listen to music wirelessly and connect devices without an audio jack to your car’s sound system – We still lament the fact that many smartphones today (especially high-end ones) don’t have an audio jack. You either need a dongle that converts a phone’s Lightening or USB charge port to an audio jack, or you need some sort of Bluetooth/wireless connectivity. If your car doesn’t already have Bluetooth connectivity an FM transmitter is a great way to stream music, podcasts and more to your car’s radio/sound system.
Have a USB charger on hand – Many FM transmitters feature one or more USB charging ports that will allow you to charge a device such as a phone while on the move. This can be a life saver in emergency situations or on long road trips where you need to keep your phone charged up.
Receive calls without having to touch your phone – Most Bluetooth FM transmitters offer more than just wireless music playing. Hands free calling is another great benefit with the transmitter taking advantage of your vehicle’s speakers. Some Bluetooth transmitters feature their own built-in microphone, while others simply utilise the one on the connected phone.
No need to share cables – If you are on a road trip with a group of friends it can be annoying to share an audio cable between devices. Bluetooth connectivity will allow multiple occupants to easily connect to the FM transmitter and switch playlists, songs, etc.
How Much Do These FM Transmitters Cost?
Before we dive into our experiences and thoughts on each FM transmitter, let’s look at how much each one costs. The following prices are what we paid for these transmitters and are just a guide. The prices may have changed since we purchased them, so keep that in mind if you notice that the current price online is different to what we have listed below.
|Scanner||Price in USD (at the time of purchase)|
|CSYLX BT-X7 Smart Bluetooth FM Transmitter||$9.98|
|IMDEN C57 Bluetooth 5.9 FM Transmitter||$17.99|
|Nulaxy KM18 FM Transmitter||$18.99|
|Nulaxy KM30 FM Transmitter||$23.99|
|Avantree CK310 FM Transmitter||$29.99|
First Impressions, Packaging & Size
There’s really not too much to talk about when it comes to the packaging on these five FM transmitters, however, the CSYLX is undoubtedly the worst. The box wasn’t in the best condition, and it looked like it had already been opened (possibly a return, but we can’t confirm).
The other four transmitters all have good sturdy packaging, but we liked that the IMDEN was encased in full cardboard packaging and there was no plastic. Below we have listed the size of the FM transmitters without the packaging. Some of them, like the KM18, were a little bit awkward to measure as they have adjustable necks/inserts.
|Scanner||Size Without Packaging (L x W x H)|
|CSYLX BT-X7 Smart Bluetooth FM Transmitter||73 x 40 x 49 mm (2.87 x 1.57 x 1.9 inches)|
|IMDEN C57 Bluetooth 5.9 FM Transmitter||75 x 32 x 32 mm (2.95 x 1.26 x 1.26 inches)|
|Nulaxy KM18 FM Transmitter||175 x 49 x 80 mm (6.9 x 1.9 x 3.54 inches)|
|Nulaxy KM30 FM Transmitter||110 x 40 x 85 mm (4.33 x 1.57 x 3.35 inches)|
|Avantree CK310 FM Transmitter||18 x 45 x 45 mm (0.7 x 1.78 x 1.78 inches)|
While the Avantree CK310 is the smallest of the lot, it is the only one that doesn’t plug into the cigarette lighter and instead gets its power from a USB cable. In our case, this meant that we had to have a cigarette USB charger and then plug the CK310 into that. A relatively minor annoyance, but something to be aware of if you don’t have a USB charger already or you don’t want to lose the ability to charge your phone from the cigarette lighter while playing music.
Avantree included a couple of 3M backings, so you can stick the CK310 where you like. However, during our tests we just let it sit in the centre console and didn’t use the 3M backing. If you hate the look of messy wires, you probably won’t like the CK310 (not a deal breaker for us).
When it comes to the actual fit, finish and form factor, we liked the IMDEN the most. It is really no bigger than a normal cigarette lighter USB charger and doesn’t get in the way of things. The plastics felt good quality and it fit securely into the lighter socket.
The two Nulaxy transmitters feature long necks that make them much bigger than the other three transmitters on this list. This makes them stick out much further from the cigarette lighter socket, but it does give them more adjustability. However, this can be really annoying if the cigarette lighter is located next to the seats, near the gear shifter/selector. Additionally, you can bump into these FM transmitters quite easily if you are shifting gears/positions, depending on the car you are driving. The KM18 was by far the worst offender here and the problem is only made worse by the fact that the connection between the transmitter and the cigarette lighter was very loose. This led to the transmitter falling out a number of times, especially on bumpy roads (an issue on all cars we tested).
Despite being the cheapest option by a good amount, the CSYLX felt no worse in quality when compared to the other four transmitters. However, the way the front of the device (where the controls are) angles back means that it will not fit correctly in some lighter sockets. On an older Volvo we had to turn the FM transmitter 90 degrees to get it to fit. This seems to be a bit of a design oversight and if you like to have everything perfect, this transmitter probably isn’t the one for you.
- Gold – IMDEN C57 Bluetooth 5.9 FM Transmitter
- Silver – Avantree CK310 FM Transmitter, Nulaxy KM30 FM Transmitter
- Bronze – CSYLX BT-X7 Smart Bluetooth FM Transmitter, Nulaxy KM18 FM Transmitter (worst option)
Connectivity and Instructions
Connectivity was incredibly easy with all five of these devices connecting seamlessly with our phones. Simply plug the FM transmitter into the lighter socket or USB port in the case of the Avantree and go into the Bluetooth settings of your phone/device. The FM transmitter should then appear in the Bluetooth settings of your device. Select the FM transmitter and it should connect. Some of the transmitters give an audible signal that they have connected to a device and some show the connection on the screen.
The only one we had an issue with was the Nulaxy KM18. It would not power on in the first vehicle we tried, however, it did work on other cars. Additionally, as the fit was loose in the lighter socket it kept on dropping out and as a result the connection would drop, and the transmitter would turn off. This was a massive problem for us, and it happened on all cars we tested. We are not sure if this is just an issue on the KM18 transmitter we received as there don’t seem to be any comments on the problem in any Amazon reviews (at least ones we can find).
When it comes to the instructions, they all told us what we needed to know. The instructions of the BT-X7 were probably the worst as some of the grammar, etc. isn’t the best. Check out the gem of a quote below to see what we mean.
“Open the music App of phone, and all kinds of App of network radio to enjoy the abundant music feast”
- Gold – IMDEN C57 Bluetooth 5.9 FM Transmitter, Avantree CK310 FM Transmitter, Nulaxy KM30 FM Transmitter,
- Silver – CSYLX BT-X7 Smart Bluetooth FM Transmitter,
- Bronze – Nulaxy KM18 FM Transmitter
Finding the Right Frequency
Once you have connected the FM transmitter to your Bluetooth device, the next step is to set the frequency on the transmitter to the same as on the radio in your car. It is important to find a frequency band that is not in use, otherwise you will get interference.
This was fairly simple to do on all devices. Some of these transmitters feature dedicated buttons for changing the frequency, while others require you to press and hold the phone button or another button until “frequency” pops up or is selected. You can then use the next song/previous song buttons to select the frequency. This extra step really isn’t much of an issue at all as once it is set you don’t have to worry about it again.
The only transmitter that we did have trouble with was the CSYLX BT-X7. It worked perfectly in the first car we used it in, however, when we tried it in other cars, we could not adjust the frequency for some reason. We are not sure if this was a fault that developed with the device, but it was very annoying and could be a dealbreaker.
- Gold – IMDEN C57 Bluetooth 5.9 FM Transmitter, Avantree CK310 FM Transmitter, Nulaxy KM30 FM Transmitter, Nulaxy KM18 FM Transmitter
- Silver –
- Bronze – CSYLX BT-X7 Smart Bluetooth FM Transmitter
Sound quality is so often a subjective thing, but I think we can all agree that muddy audio with lots of interference is a bad thing. Bluetooth FM transmitters used to get a bad rap for poor quality audio, but what about the five ones we are looking at in this guide?
At some point we will update this guide with recordings of each FM transmitter, but for now we will just talk about our experiences. We will also do more testing over an extended period of time, so we will include our findings from that as well.
Without a doubt, we feel that the Avantree CK310 has the best audio quality of the lot. The sound was definitely the cleanest, but unfortunately there was still some static/hiss noises in some songs (not all).
The worst of the bunch was the BT-X7 from CSYLX. We found the sound to be muddy and there was quite a bit of interference noise, especially on base heavy songs. The other three FM transmitters all sounded roughly the same and we couldn’t put one over the other.
None of the transmitters sounded quite as good as a cable connection, but we expected that and were really surprised at just how close they got (apart from the BT-X7). You will get some interference noise with all these transmitters, so do keep that in mind if you are wanting 100% clean sound. We never found it to be a problem, apart from on the BT-X7.
One other issue to keep in mind is that the audio volume can be quite low through these FM transmitters. Turning up the volume on your vehicle’s sound system will still let you get to more than acceptable levels, but if you are one of those people who loves to make your car shake with your epic playlist it may be a problem (This problem was never an issue for us).
The audio problem can be an issue if you like to switch to the regular radio frequently as it can be a nasty surprise if you forget to turn the volume back down on your vehicle’s sound system.
A feature that makes the KM30 stand out above the rest is its ability to tune the bass and the treble. While the controls are fairly simple, it does make more of a difference to the sound than we expected. There is a decided button for the treble and nice red one for the bass. When you press one of these buttons, the screen will display the levels for the treble and the base. You can then use the volume knob to adjust the level for the one you pressed. While I don’t see myself using this feature that often, it is a nice thing to have.
- Gold – Avantree CK310 FM Transmitter, Nulaxy KM30 FM Transmitter (not quite as good as the CK310 but the ability to tune the bass and treble is nice).
- Silver – IMDEN C57 Bluetooth 5.9 FM Transmitter, Nulaxy KM18 FM Transmitter
- Bronze – CSYLX BT-X7 Smart Bluetooth FM Transmitter
There really isn’t much to say here that wasn’t covered above in the sound quality section. Most buyers will be more than happy with the call quality of each of these transmitters and the built-in microphones do the job (just don’t expect exceptional audio quality).
The call buttons on all these products work seamlessly when you want to answer or refuse a call, and we did not find any usability issues.
All FM transmitters performed roughly the same, although you can say that the Avantree has the best sound quality as we mentioned in the previous section.
Both the Nulaxy KM30 and the IMDEN C57 feature QC (Quick Charge) 3.0 ports, so charging is fairly rapid off these transmitters. They both also have an additional USB port that can be used to connect a device such as a USB thumb drive with music on it. While charging through these additional USB ports is much slower than with the QC 3.0 ports, they still can be used to provide a little bit of juice to a device.
Quick Charge 3.0 theoretically allows you to charge a phone with a 3,500mAh to 4,500mAh battery to 80 percent in as little as 35 minutes when the battery is fully depleted. This is a nice feature to have, especially if you forget to charge your phone.
Like the Nulaxy KM30 and the IMDEN C57, the BT-X7 from CSYLX features two USB ports, a 3.1A one for charging and a 1A one for music. Once again, the 1A one does provide charging capabilities, but at a much slower rate. The main charging port is more than good enough and provides fast enough charging for us.
The KM18 features a single 5V 2.1A USB port for charging, which makes it a bit more limited than the three transmitters we have already talked about in this section.
Finally, the Avantree CK310 does not feature a charging port and instead uses up a USB port just to power the device. This means that if you only have one USB connection in your vehicle, you will have to pick between charging your device or playing music through the CK310. This is a big downside to an otherwise great device.
- Gold – Nulaxy KM30 FM Transmitter, IMDEN C57 Bluetooth 5.9 FM Transmitter
- Silver – CSYLX BT-X7 Smart Bluetooth FM Transmitter
- Bronze – Nulaxy KM18 FM Transmitter
- No ranking – Avantree CK310 FM Transmitter
Screen/Display and Other Features
Both Nulaxy transmitters feature a small 1.8-inch Colour display that shows things such as the song that is being played, which device it is connected to and more. We prefer the display on the KM30 as it shows a bit more, but to be honest we stopped looking at either display after the initial appeal had worn off. However, these displays are handy if you have a passenger who wants to see or know what song is being played.
Unfortunately, the displays on the KM30 and KM18 are quite reflective, so a bit of sunlight can make them unreadable. One other benefit of the KM30 and KM18 are their SD card slots. No other transmitter in this guide has this feature and while it is unlikely we would use it ourselves, it may be of use to some buyers.
The displays on the other three transmitters are all very simple and only tell you things like the frequency, setting, etc. However, the lack of display does make these transmitters smaller than the Nulaxy ones.
- Gold – Nulaxy KM30 FM Transmitter
- Silver – Nulaxy KM18 FM Transmitter
- Bronze – IMDEN C57 Bluetooth 5.9 FM Transmitter, Avantree CK310 FM Transmitter, CSYLX BT-X7 Smart Bluetooth FM Transmitter
Best Bluetooth FM Transmitter for Cars
So, which one of these five FM transmitters is the best in our opinion? While we are still going to do some longer-term tests (and we will update this guide accordingly), we feel that the IMDEN C57 and the Nulaxy KM30 transmitters are probably the best.
The sound quality of both transmitters is good, and they offer good charging capabilities, which is quite important to us. While the KM30 has more features and a handy 1.8-inch screen, the C57 is a much nicer form factor and is unobtrusive. The biggest downside to the KM30 is that it sticks out quite far from the cigarette lighter. For now, we are going to call it first equal for these transmitters and you really can’t go wrong with either option.
In second place we are going to have to give it to the Avantree CK310. While we feel that it did have the best audio, the fact that it takes up a charging port is a dealbreaker for us if you only have one USB output port. Additionally, if you have an older car and don’t have a cigarette lighter USB charging device, you are going to have to buy one, adding more to the price. The last issue we have with this transmitter is that it just looks messy. You also have to find a place to stick it or just simply let it sit on the centre console.
The Nulaxy KM18 and the CSYLX BT-X7 come in a distant third and are firmly in our ‘no buy’ category. While the KM18’s sound quality is fairly good, the fact that the connection into the cigarette lighter socket is so bad is a deal breaker. It falls out when you go over bumps and the thing is just an eyesore. You also bump into if the lighter socket is next to the seat/shifter, which is really annoying.
CSYLX’s transmitter doesn’t have the issues of the KM18, but the sound quality was definitely worse than the other four transmitters and the interference noise did annoy us after a while. Additionally, we had problems with adjusting the frequency and the angled nature of the front of the transmitter means that it may not be compatible with all vehicles (or it needs to be turned like when we used it in an older Volvo 940).
So, there you have it. The best Bluetooth FM transmitters in our opinion are the Nulaxy KM30 and the IMDEN C57. The Avantree is acceptable if you have a spare USB port, but avoid the Nulaxy KM18 and the CSYLX BT-X7.
To help you better decide which of these products (if any) is right for your needs, we’ve also put together a short FAQ section below which will be expanded on in the coming weeks. We are also hoping to release a video version of this review (we are just finalising how it will work from the perspective of recording audio quality).
Bluetooth FM Transmitter FAQs
Do Bluetooth FM Transmitters Work?
As you can see from this article, bluetooth FM adapters do work. However, what is important is that you go in with realistic expectations. If you are expecting “studio quality” sound from your FM transmitter, then you’re going to be disappointed.
Realistically, an FM transmitter is a ‘last resort’ for modernising your car’s audio and connectivity capability.
If you have an AUX adapter, for example, then you are better off to pay your music through AUX (either using the headphone jack on your phone, an adapter for modern phones like iPhones that only have one input/output, or even getting an AUX to bluetooth adapter if you are really committed to the idea of using bluetooth). Even if you have a tape deck, you’ll probably enjoy superior sound quality and simplicity by using a tape deck to AUX adapter – we will be reviewing some of these in the not-too-distant future so keep an eye out for that.
If your car has a standard DIN or Double-DIN stereo, then you are better to look to replace your entire head-unit if this is within your budget – and the good news is that these days there are many affordable options available that come with features such as Apple Carplay and Android Auto. This will get you far better audio quality and functionality than any bluetooth FM transmitter will.
Some cars – like the Fiat Stilo Abarth used as one of the demonstrators for this review – have non-standard dimension stereos or are otherwise difficult to have the factory unit replaced to something more modern. The Stilo has no AUX input, and no bluetooth capability, so an FM adapter is the next best option.
What Alternative Options Are There?
Depending on the type of stereo/head-unit installed in your car, you might wish to consider:
- AUX to bluetooth adapter
- AUX adapter and directly plugging in your phone or other device (possibly via an adapter if you have a more modern smartphone that lacks a headphone jack)
- Tape deck adapter – there are AUX and bluetooth options available, we will be reviewing these in the near future
- Upgrading your head unit
- Searching to see if there is any model-specific upgrade for your car. For example some Audi stereos from the mid 2000s could be upgraded to have AUX capability via a special type of adapter.
Are Bluetooth FM Transmitters Legal?
Long story short, any transmitter you buy “off the shelf” that is designed for the purpose of allowing you to play music in your car is generally going to be legal. There are some complex laws (depending on your legal jurisdiction) that govern radio frequencies etc, and higher powered transmitting devices can be illegal in some countries.
While we are not lawyers – and therefore cannot take any responsibility if for some strange reason you do get in legal bother for using a bluetooth transmitter – chances are you are going to be perfectly fine.
If you are able to walk into an electronics or auto shop in your country and buy a Bluetooth FM transmitter for your car off the shelf, then this category of product is most likely going to be legal in your jurisdiction.
In the United States, this category of device is governed by the “47 CFR 15” (often called Article 15) part of the Federal Communications Commission (FCC) rules regarding unlicenced transmissions. Basically, the device in question – e.g. your new transmitter that you might have bought after reading our review – must comply with certain technical specs e.g. having a maximum field strength of 0.01 microwatts.
Will A Bluetooth FM Transmitter Drain Your Car Battery?
Most cars have a 12V socket (often referred to as the ‘cigarette lighter socket’) which switches off when the car is turned off, as the socket is really powered by the alternator while the car is running and not the battery. Therefore, you shouldn’t have any issues with the transmitter draining your battery as there won’t be any drain when the car is off.
If you have a weak battery or alternator issues with your car, then there is always the risk of complications, but provided your car is in good shape then a bluetooth transmitter plugged into the 12v is not going to cause any issues.
Please note that some cars do have 12v socket(s) that stay live even when the car is switched off. In this case there is the risk of “parasitic drain” on the car battery, but the draw from an FM transmitter plugged into the 12v socket is small and so you are probably fine to leave it, provided you are using the car regularly enough to charge the battery via the alternator.
Check your owner’s manual to see if your car has a live 12v socket when the ignition is off, or you can test by connecting up something like a phone charger and testing to see if the phone still charges when the engine is off.
If you have a car where the socket stays live all the time, then we would advise you to remove the transmitter when the car is powered off, or at least switch off the device … especially if you don’t use your car frequently or it is going to sit for a long period of time.
Leaving an interior light on is far more likely to be a battery drain culprit!
What Is The Best Station/Frequency To Use With An FM Transmitter?
One of the most common questions we see asked about this type of device is what the best station/radio frequency to tune into is if you want good audio quality with minimal interference.
The truth is that this depends greatly on your location. However, a general rule of thumb is that the best station/frequency to use is one that is vacant, i.e. not being occupied by any other broadcast.
Different locations (not just countries but even states, cities and towns) can have different “vacant” frequencies. This is why sometimes you might have an issue where you tune your transmitter to a frequency, and then find that you get interference when going on a long road trip into a different state or county where that “empty” frequency is being used.
Our view is that you are best to start with the specific manufacturer instructions from your device and then work from there.
If you’re based in the USA, then we found this handy (albeit rather old-fashioned looking) tool that helps you find vacant frequencies based on your ZIP code and state, as well as what the next-best option(s) are if there are no vacant frequencies available. There are also some handy extra tools for international users. Check it out at https://radio-locator.com/cgi-bin/vacant
How Do Bluetooth FM Transmitters Work?
Long story short, the “bluetooth” part of the device connects your phone to the device itself (via bluetooth, funny that) which is a common technology/protocol for wirelessly sharing data across short ranges. This is no different to how your phone might connect to a bluetooth headset, or how you might connect a bluetooth keyboard to your computer.
The audio signal/data goes from your phone to the transmitter device via bluetooth connection.
From here, the “FM transmitter” part kicks in, and the device broadcasts the audio signal on a specific radio frequency. Your car stereo is then able to pick up the signal via this radio frequency, just like you might tune into any radio station in your area.
While there is a lot more to it from a technology perspective, that is the basic functionality of how bluetooth FM transmitters work.
Are There AM Radio Transmitters For Classic Cars?
What if your car is so old that it only has an AM radio? This is the case with some “vintage” classics from the early-to-mid 20th Century. Blaupunkt introduced the first FM car radio in 1952, but this technology didn’t really catch on until the 1960s. Therefore, there are older cars on the road that lack FM radio capability.
Many vintage car enthusiasts don’t want to spoil the originality of their cars by adding aftermarket stereos that might require cutting out parts of the dashboard or otherwise altering the car (that is totally understandable!)
In this case, are there AM radio transmitters available for classic cars?
Let’s start with the bad news.
The bad news is that getting an AM radio transmitter that allows you to play audio from your phone or device through your vintage car radio is not as easy as if you have FM capability. With FM capability you have a plethora of options – such as those reviewed in this article. With AM the choices are much more limited.
The good news is there are some AM radio transmitters available.
The RediRad is one such product we found online, which is specifically designed to allow for smartphone connectivity to your vintage AM car stereo without needing to make any permanent modification to the car. One issue with the RediRad is that it works with an AUX input into the device, which then broadcasts to your car radio – not all modern phones have an AUX output (headphone jack) but you might be able to work around this by using a USB-C/phone charger to AUX adapter. Another option would be to buy an MP3 player like an older iPod with AUX output and store your music on that and then playback directly.
We also found this interesting looking product on Etsy, which some purchasers had indicated worked for their old cars.
Basically, if you have AM radio functionality only then your options are more limited … but you still have options! However, it might just be easier to ‘bite the bullet’ and cart around a portable speaker with you, such as a UE Boom, that you can much more easily connect to your phone for audio playback.
Should You Use A Bluetooth FM Transmitter If You Can Use AUX?
A number of cars from the mid-2000s onwards come with AUX connectivity (3.5mm headphone jack) but no Bluetooth capability.
We get a lot of questions from owners of cars of this sort of vintage, wondering if a Bluetooth FM transmitter is a better choice than using the AUX input.
Our take is simple – if you have an AUX input, then it’s better to use that. You can always purchase a Bluetooth AUX adapter so you get the same kind of functionality as an FM transmitter but with superior connection reliability and audio quality.
FM transmitters are a decent option when you have no other choice, but AUX is almost always going to be more reliable and offer you better quality sound. The other advantage is that AUX adapters tend to be more affordable than FM transmitters.