It's a mesh network that relies on beaconing to devices with Bluetooth enabled or more preferably Apple devices that are UWB-capable (U1 chip) which in return gives more precise tag localization. You can track tags from your either phone or tablet; these so far aren't visible on iCloud page IIRC.
I've got one but it seems to be activating only when Apple devices are around
Similar devices exist around - Samsung for example has own line of such tags
Basically most mobile Apple devices are enrolled in a network and anytime that an iPhone is near an Airtag, that network relays the location. It is essentially automated crowdsourcing of the location of stuff.
pndy|2 years ago
I've got one but it seems to be activating only when Apple devices are around
Similar devices exist around - Samsung for example has own line of such tags
https://en.wikipedia.org/wiki/Bluetooth_Low_Energy_beacon
https://en.wikipedia.org/wiki/AirTag
MattGaiser|2 years ago