We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-21 · 6 min read · Independent comparison
If you want a familiar, lightweight pair of sweat-resistant Bluetooth earbuds for the gym and your daily commute, choose Koss BT115i; if you need open-ear headphones that survive full underwater swimming and can play music without a phone, choose PSIER Bone Conduction Headphones.
• Koss BT115i — biggest strength: A traditional in-ear design with in-line remote controls and a sweat-resistant build, which makes it a natural fit for running, lifting and everyday listening.
• Koss BT115i — biggest trade-off: It's Bluetooth 4.2 only, not waterproof for swimming, and it depends on a connected device for every second of playback.
• PSIER Bone Conduction Headphones — biggest strength: IPX8 waterproofing plus 32GB of built-in MP3 storage, so you can swim with music and leave your phone on the deck.
• PSIER Bone Conduction Headphones — biggest trade-off: An open-ear bone conduction design leaks sound and gives up the noise isolation that in-ear buds provide, and there's no wired remote to fiddle with — controls are touch-based.
• Who each pick is for: Koss BT115i for the runner or gym-goer who wants classic buds with physical controls; PSIER for the swimmer, cyclist or open-ear convert who wants to stay aware of their surroundings.
The BT115i is Koss doing what Koss has always done: simple, functional wireless earbuds with a wired-style remote hanging on the cable. You get Bluetooth 4.2 wireless with a 10-meter range, an in-line microphone and remote for play/pause, track skipping, volume and answering calls, and a set of three silicone tip sizes (small, medium and large) so you can dial in the fit. There's also a cable management clip that slides along the cord to keep things from tangling — a small detail, but one that matters if you've ever yanked a bud out of your ear mid-run.
Battery is where the numbers get interesting. The spec sheet lists a 6-hour average battery life and a 6-hour charge time. That's the honest picture: you get roughly a workout-and-commute's worth of playback per charge, and you'll want to plug in via USB-C overnight. The 5.8mm dynamic drivers with a frequency range of 18–20,000 Hz and 16-ohm impedance are typical of small in-ears — fine for podcasts, pop and gym playlists, not a critical-listening setup.
Who should skip it: Swimmers, anyone who wants to leave their phone behind, and anyone who needs all-day battery. With no waterproof rating for submersion and no onboard storage, the BT115i is a phone-tethered product from the moment you turn it on.
PSIER Bone Conduction Headphones: Who It's For
The PSIER S18 is a completely different animal. It's an open-ear bone conduction headphone, which means the drivers sit outside your ear canal and vibrate through your cheekbone instead of plugging your ears. The practical benefit is awareness: you hear traffic, training partners and your surroundings while music plays. The trade-off is the same one every bone conduction model makes — you give up isolation, and people around you may hear some of what you're playing.
The headline feature is durability. The IPX8 rating means it can be submerged up to two meters for an hour, which is why PSIER pairs it with 32GB of internal MP3 storage — enough for thousands of songs, with support for MP3, WMA, FLAC, APE and WAV files. You switch to MP3 mode with a double-click of the power button, and that's the mode you use in the water, since Bluetooth won't transmit reliably underwater. The 14mm bone conduction drivers, meanwhile, handle the audio, and there's a built-in microphone for calls plus compatibility with the Boean app for EQ tweaking and AI music generation.
Battery life is listed at 8 hours in Bluetooth mode with a 2-hour magnetic charge — noticeably better than the Koss on both ends. The package also includes an adjustable strap for different head sizes, and the silicone cushions are designed to sit gently against the skin for long sessions.
Who should buy it: Swimmers first and foremost. This is one of the few designs that genuinely works underwater, and the MP3 mode means no phone, no pouch, no problem. It's also a strong pick for cyclists, runners in traffic, and anyone who finds in-ear buds uncomfortable after an hour.
Side-by-Side: Which Should You Choose?
• Best for swimming → PSIER. IPX8 submersion plus MP3 mode is a combination the Koss simply doesn't offer.
• Best for battery life → PSIER. 8 hours of playback and a 2-hour charge beats the Koss's 6-hour life and 6-hour charge.
• Best for gym and running with a phone → Koss. Sweat resistance, three tip sizes, a cable clip and physical in-line controls are made for movement.
• Best for phone-free listening → PSIER. 32GB of onboard storage means you can leave the phone at home.
• Best for staying aware of traffic → PSIER. The open-ear design lets ambient sound in by default.
• Best for sealed-in, private listening → Koss. In-ear buds keep your audio to yourself; bone conduction does not.
• Best for control simplicity → Koss. A remote with real buttons beats double-taps and touch gestures when your hands are sweaty.
• Best for a single do-everything pair → PSIER. It covers land and water, whereas the Koss covers land only.
If I had to pick one, I'd buy the PSIER Bone Conduction Headphones. In my opinion, the IPX8 waterproofing, the 32GB of built-in storage and the 8-hour battery make it the more versatile product — it handles swimming, running and commuting, and it doesn't fall apart the moment moisture shows up. The Koss BT115i is a perfectly sensible pair of sweat-resistant buds with controls I genuinely prefer, but it can't follow you into the pool and it can't play a single song without your phone. For most people reading a comparison like this, the PSIER covers more of real life.
FAQ
Yes. It has 32GB of internal MP3 storage for roughly 4,000 songs, and you switch to MP3 mode with a double-click of the power button. That's also the mode you must use underwater, because Bluetooth doesn't transmit reliably through water.
The PSIER, on paper. It's listed at 8 hours of playback with a 2-hour magnetic charge, versus the Koss BT115i at 6 hours of battery life and a 6-hour charge time. For long days out, the PSIER needs less babysitting.
They're different, not ranked. In-ear buds like the Koss seal your canal, so you get more bass and isolation. Bone conduction like the PSIER keeps your ears open, so you trade low-end punch and privacy for awareness and comfort. Pick based on where and how you listen, then check the current price on Amazon before you commit.
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