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A tracker to find your lost item or keys Answered

Hi guys, i want to make a tracker device which can track keys or items, but i have no idea what sensors do i use to work in a small parameter, any help? 


RFID is your best bet, but only if you assume that you are in the near vicinity of wherever you "lost" the item (e.g., you're at home, and you just don't remember where you put the keys down). It is short range, and the RFID "rice" doesn't need any power: you walk around with the reader, waving it about, and eventually it goes off.

Low-energy Bluetooth (BLE) gives you a 50 meter range (bigger than a house), but at the expense of having to include battery power in the object (key fob).

Caitlinsdad's idea of a radioisotope source is philosophically cool, but rather impractical from a safety standpoint. Penetrating/ionizing radiation (like gammas or betas), falls off faster than 1/r2 due to atmospheric scattering (so not as good as a simple transmitter/receiver), and also presents a theoretical hazard which would run you afoul of regulatory and law enforcement agencies.

The biggest problem is that the keys would need a possibly obtrusive fob on it to constantly send out a signal or receive a signal from the homing device to actuate a light or buzzer. The batteries would run out when you need it. They did have those As seen on TV clapper key finders. Tracking with radio signals would need a lot of gear to pinpoint something very directional like where your keys are. Far range RFID scanners would probably be no better. I guess you could plant a radioactive source on the keys and track it down with a geiger counter. Maybe someone else has ideas. Good luck.