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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-30 · 7 min read · Independent comparison
• COOMAX Mini Hidden Spy biggest strength: a 0.8g in-ear earpiece with an inductive loop, a microphone and a one-button call control that works with phones, tablets, Kindles, eReaders and anything with a standard 3.5mm jack.
• COOMAX biggest trade-off: it runs on a single SR416SW/337 button battery for roughly 3–5 hours, uses analogue magnetic/RF induction reception, and the design itself warns you not to use it for music.
• LVY Headphone Amplifier 3.5mm biggest strength: a two-stage gain switch, load impedance support from 16–300Ω, SNR above 120dB and 0.004% distortion, with more than 5 hours of amp use per charge.
• LVY biggest trade-off: it is a wired inline amp, not a headphone and not a player — it needs a source device and your own headphones, and it adds a small box to your pocket or desk.
• Who each pick is for: the COOMAX suits someone who wants discreet, hands-free audio and call pickup; the LVY suits someone who already owns good headphones and wants them driven properly on phones, laptops and MP3 players.
The COOMAX Mini Hidden Spy is built around one idea: audio you can hear without an earpiece being visible. The earpiece itself is microscopic — 5x7x10mm, 0.8g, anatomical in-ear shape, 100 ohm impedance, 110dB sensitivity and a 20Hz–20,000Hz range. It's a magnetic/analogue receiver, with an inductive loop that goes around your neck and plugs into whatever drive equipment you're carrying, such as a phone or radio. The microphone and one-button control mean you can also take calls and control a smartphone without pulling anything out of a pocket.
Compatibility is broad on paper: iPhones (with a lightning-to-audio adaptor), Android phones, tablets, Kindle, eReaders, and any portable device that has a standard 3.5mm jack. It also lists support for phone calls, FM radio and MP3 players. If your goal is a hands-free, low-profile way to hear prompts or stay on a call while your phone stays where it is, this is the category the COOMAX sits in.
Skip it if you want to listen to music. The manufacturer's own note is explicit: because of the RF wireless working principle there's a slight current noise, and it is not recommended for music. That same sheet tells you to keep it away from computers, speakers, TVs and fridges because of possible interference. Add a 3–5 hour battery life on a replaceable button cell, a 5-hour charge time figure, no noise control, and plastic construction, and you have a device that is specialised rather than general-purpose. In my opinion, this is a tool for a narrow job — not an everyday music headphone.
The LVY Headphone Amplifier 3.5mm does the opposite job. Instead of replacing your headphones, it sits between your device and the headphones you already own and pushes a stronger, cleaner signal into them. The headline numbers are the two-stage gain switch, which boosts the input signal into the amp circuit so headphones perform closer to their potential, and a load impedance range of 16–300Ω — wide enough to cover typical in-ears up through many full-size models.
The signal path is where it earns its keep: SNR above 120dB and distortion of 0.004%, which is the spec-level reason the output should be not just louder but sharper. Input and output are both 3.5mm AUX, so you plug the source into one end and your headphones into the other, and it works with MP3 and MP4 players, phones, laptop computers and other 3.5mm digital devices. It's compact at 3.6 x 0.5 x 1.9 inches and 0.16kg, in a matte black finish, with more than 5 hours of amp use, a 2-year warranty, and no plug of its own — it charges over its own connection rather than needing a wall adapter in use.
This is for the person whose headphones sound thin, quiet or lifeless straight out of a laptop or a phone, and who wants a pocket-sized fix rather than a new pair of headphones. It is not for you if you want a wireless experience, if you want something to make calls with, or if you want a device that works entirely on its own without a source and a pair of headphones. It also won't do anything for Bluetooth headphones — the 3.5mm jack is the whole point.
Side-by-Side: Which Should You Choose?
• Best for discreet, hands-free audio → COOMAX Mini Hidden Spy. The 0.8g in-ear earpiece plus inductive loop is designed to stay out of sight while you take calls or hear prompts.
• Best for making existing headphones sound better → LVY Headphone Amplifier 3.5mm. Two-stage gain and 16–300Ω load support are built exactly for that.
• Best for music listening → LVY Headphone Amplifier 3.5mm. The COOMAX's own documentation advises against using it for music because of the current noise inherent to its RF induction design.
• Best for taking calls → COOMAX Mini Hidden Spy. It has a built-in microphone and a one-button call control; the LVY has no microphone and no call controls at all.
• Best for devices with a plain 3.5mm jack → both, but differently. The COOMAX connects to the source and feeds one tiny earpiece; the LVY sits inline between the source and your headphones.
• Best for clean, low-distortion signal → LVY Headphone Amplifier 3.5mm. A 0.004% distortion figure and SNR above 120dB are the specs that matter here.
• Best for a low-profile, wearable form factor → COOMAX Mini Hidden Spy. At 5x7x10mm and 0.8g it disappears in the ear; the LVY is a 3.6-inch box you carry or set down.
In my opinion, most people reading this comparison should buy the LVY Headphone Amplifier 3.5mm (ASIN B07WDXDNM1). It solves a problem almost every headphone owner actually has — headphones that don't sound their best out of a phone or laptop — and it does it with specs that make sense: two-stage gain, 16–300Ω support, SNR above 120dB, 0.004% distortion, over 5 hours of use and a 2-year warranty. The COOMAX is genuinely clever at one narrow thing, but that thing is covert listening and calls, and its own notes rule out music. If that narrow job is exactly your job, the COOMAX is the right tool. For everyone else, the LVY earns its place in the bag.
FAQ
how to listen to two devices at once with headphones
how to unpair headphones from all devices
That step only applies to Bluetooth headphones, and neither product here is Bluetooth. The COOMAX uses RF wireless with an inductive loop, and the LVY is a wired 3.5mm amplifier, so both are "disconnected" simply by unplugging the cable or loop. If you're asking about a different Bluetooth headset, the reset is done from that headset's own pairing menu.
how to disconnect headphones from all devices
With these two, disconnecting is physical, not digital. Unplug the LVY's 3.5mm AUX cable from your phone or laptop and it's out of the chain; pull the COOMAX loopset cable from its drive equipment and the earpiece stops receiving. There's no stored pairing list to clear on either one.
how to make headphones forget all devices
There's nothing to forget here, because neither the COOMAX nor the LVY stores paired devices. The COOMAX works through magnetic/analogue inductive reception from a connected source, and the LVY passes signal through a 3.5mm jack. If you want the closest thing to a fresh start, just remove the battery from the COOMAX earpiece or unplug the LVY.
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