Found it!

Almost two years ago, I managed to lose my BT headset module. Now I found it! Apparently it ended up very near the place I looked for it at, just a meter or so from where I tried to look for it,  near a wall. As the spring plants today hadn't grown yet so it was really standing out there.

After few moments of thought I tried charging it with typical wall USB charger. Surprisingly, it lit up, indicating being charged. Unfortunately it stopped charging very quickly, which I considered bad omen already. So next attempt - turn it on.

No luck. It's dead. Next few charging attempts ended up with similar fate - tries to charge, then stops very soon - can't. Not very surprising, really, this was on when I lost it, so it would have drained its battery very quickly, and after that it was allowed to drain the battery further for almost two years. If it weren't dead, I'd had been more surprised.

So, next thing was to tear it apart, to see what's inside. My first guess: One PCB with one to three active chips and a battery.

I thought that the enclosure might be ultrasound-welded or something like that, but no, it opened way too easily for that. Just snapped together. Absolutely not even water-resistant, really, but then again, I don't think that it even advertises as such, so no problem there.

Snapping it open, first glance was pretty much what I expected. One PCB, with buttons, leds, few passives and PCB antenna at the end.

Taking out two tiny screws, we get to see the other side. Battery and rest of the PCB components. Curiously batter could have been larger (I'd really want that!), but guess they thought 4-ish hours is enough. Hint: It isn't.

On PCB the main chip appears to be ISSC Technologies' IS1681S chip. With brief search, I found IS1690S datasheet, which, unsurprisingly, is a small BLE 3.0 chip with 8051 controller built in (is there a place where 80C51 isn't -- that chip is amazingly common, and amazingly powerful too, considering its roots in early 1980s). The other chip there seems to be 24C34 (I don't have my microscope handy at the moment), which would mean I2C EEPROM for storing pairings and other such data.

And that's about it. Unlike devices of 80s and 90s, these days this is way too common setup. Dedicated chip, with few support components, and not much else. Granted, this allows to bring the price down, but it's still kinda let down...