An example of what the 24259 mailbox sensor looks like in action:
It has a tamper sensor built in so if anyone tries to remove/tamper with it, it’ll send a Tamper notification to ST which can be processed with a compatible SmartApp like this one to notify you or trigger a siren: [RELEASE] Security System: Intruder Alert with Actions - Entry Delay, Exit Delay, Countdowns, Keypads, Lights, Alarms, Pictures/Cameras, Routines