Hi swhksw,
Welcome to the Apple (user-to-user) Community.
Re: how long is ‘a period of time’ here?
and
will that AirTag emit a sound when my family member drives my car?
Thank you for posting your AirTag query to the Apple Community.
Am no expert on AirTag, yet your query surely deserves some response.
Not having had AirTag experience myself, I do not know the answers.
Fortunately Apple Support documents quite a lot of detail in online articles etc,
and you may find some answers from the links and videos provided. below:
What to do if you get an alert that an AirTag, Find My network accessory, or set of AirPods is with you - Apple Support
Locate an AirTag or other item in Find My on iPhone – Apple Support
https://www.youtube.com/watch?v=mGh7-IuPRR4
https://www.youtube.com/watch?v=I1LdbZdCRzI
Online Article: Apple introduces AirTag - Apple
"If AirTag is separated from its owner and out of Bluetooth range, the Find My network can help track it down. The Find My network is approaching a billion Apple devices and can detect Bluetooth signals from a lost AirTag and relay the location back to its owner, all in the background, anonymously and privately.
Users can also place AirTag into Lost Mode and be notified when it is in range or has been located by the vast Find My network. If a lost AirTag is found by someone, they can tap it using their iPhone or any NFC-capable device and be taken to a website that will display a contact phone number for the owner, if they have provided one."
All the best :-)