How to make a keychain to find things?

Question

Do it yourself

Hello! The idea, of course, is never new, but I would like to do it. I want to collect a keychain and small stickers/pendants something else. More precisely, how: you hook the pendant to the thing, and when you can’t find the thing, you poke the button on the keychain and the pendant beeps until you press the button on the keychain again. Buttons - numbers. That is, each suspension also has its own number, so that only the desired suspension would squeak, if there are several of them. I hope I didn't explain too harshly, because I don't even know how to put it all together.

Answer 1

ibeacon
Everything has long been invented.
Typical performance characteristics:
Size: 4.6 × 2.5 × 0.3 cm
Battery type: CR2016
Battery life: 1 year
BLE chipset: RF 51.822
Response time: from 10 ms to 10 sec
Dialogue code encryption: yes
Case type: collapsible
Cost: 1200
rubles Chinese ready-made keychain costs 500 rubles.
There are tons of radar apps for phones.

Answer 2

Poverty advice:
It remains to find a reader.