Looking for ways to detect gps/Lte style trackers using handheld equipment

Iam looking into ways to detect different types of gps trackers, whether they operate off realtime gps signal or a simcard with lte celltower data.
i've got a flipper-zero i'm tinkering with discovering BTE signals, but many devices only report home once, very quicly at given intervals. is there anywhere i can find more info on this topic on ways to detect if a locator is nearby aside from being the intended recipiant?