By what principle does the AirTag work? [closed]

I hope to understand it so that I can also tell whether the following situations work:

First of all, does an AirTag talk to any unencrypted Wifi or cellular tower, or random people who walk by and have the BlueTooth turned on?

So by understanding what principles it works by, then I hope to know whether the following situations can work:

1. If I want the AirTag to be able to tell where my car is parked, or where that AppleTV remote control (with the AirTag attached) is, and I had an iPhone near me all the time.

2. If I leave an AirTag in my car's cup holder, and yesterday night, I parked my car 2 streets way, and I didn't have my iPhone with me, so today, can I use my iPhone to find my car? What if the car is more than 200 or 500 feet away?

3. What if the AirTag is attached to a Belkin string attachment and is taped to the back of the Apple TV remote control. Then if the remote is dropped under the bed and is out of battery, can the AirTag still tell where it is when the battery has run out of power?

4. What if our cat or dog took the key and the AirTag, and bury it somewhere in the backyard or in a park nearby? So all this time, there was no iPhone nearby (assuming I am not at home).

No, AirTags do not communicate over WiFi (unencrypted or encrypted), nor does it communicate with cell towers. It does communicate over Bluetooth and UWB, and the signals it emit can be received by random people walking by, if they're within range.

Your situations:

1. Yes, AirTags can help you pinpoint the location of your AppleTV remote with an AirTag attached to you. It is best at doing so if you have a newer iPhone (11+). For your car it depends on how big the parking lot is, and how often other people will walk around the parking lot near your car.

2. Yes, you can come back the next day to locate your AirTag even though you didn't have the phone with you when you left the AirTag. If the AirTag is so far from you that you cannot receive its signals, you must rely on some other iPhone user being sufficiently near the AirTag at some point.

3. Your question is a bit ambigious. The use of the Belkin string attachment has no impact on whether or not you can find the AirTag. If you mean that the AppleTV remote has run out of battery, that again has no impact on whether or not you can find the AirTag. If the AirTag itself has run out of power, then you cannot use the very precise location method that shows you the angle and distance to the AirTag. It is possible to see the last known location of the AirTag on a map even when out of battery. Note that AirTags have a fairly long battery life.

4. This depends on how deep the AirTag is buried and what kind of material is on top of it. The AirTag does not know it is buried - it will still emit its signals, and if there's a receiver (i.e. someone with an iPhone) in range, you can get notified about the position of the lost AirTag.