What do you mean by alarm? There's plenty of battery powered door sensors and such to get alerted if door opens, same with motion. If you're looking for trailer disconnect alarm look into bike lock alarms and use with breakaway cable.
If wanting to locate if stolen then an air tag is cheap and great.
Victron can use usb GPS and they have geofencing so I can be notified if my RV moves from my driveway. Needs cell though.
Any simplisafe or other type of alarm for a house will work fine in a trailer. Same with camera system.
