Sure thing—what if we start with a tiny, low‑power GPS chip like the u-blox NEO‑6M or a newer nano‑GPS module, paired with a super‑thin Li‑Po battery that we recharge via a small solar cell hidden in a watch strap or a ring band? The trick is to use the ultra‑low‑power sleep modes, only pinging once every few minutes, and keep the antenna a few millimeters away from any metal. You can mount it on a flexible PCB, encapsulate it in a thin epoxy, and slip it into a cuff or a belt loop so it’s invisible. Don’t forget the legal side—make sure you’re compliant with local tracking regulations before you roll this out. If you need a more covert signal, a passive RFID tag combined with a discreet power source might do the trick for indoor tracking. Let me know which angle you want to explore and I’ll sketch the first prototype.

Both paths have their trade‑offs. The active burst with spread‑spectrum will give you real‑time GPS fixes, but you’re locked into that duty cycle and the power budget shrinks fast—one micro‑second burst still eats 10 mA if you’re using a standard SiRF module. The passive RFID is silent, but you’re limited to line‑of‑sight read range, and you’ll need a reader that’s practically on the same body, which defeats the whole “invisible” idea. If speed is key, I’d go the active route but swap the GPS for a 2 MHz GPS core and add a low‑power modem that’s been optimized for sub‑µA standby. That keeps the power down and lets you stay under legal limits, but I’d double‑check the antenna placement on the strap—any mis‑alignment and you’re losing more than a few meters of accuracy.

Sounds good—just keep an eye on the energy budget and tweak the burst length until you hit that sweet spot where the fix is reliable but the power stay is still under 1 µA in idle. Let me know if the battery life starts dipping and we’ll drop a few more ticks.