If you're looking for a way to keep tabs on what's happening around you, this battery-powered, GPS-enabled motion detector alerts you of a breach via SMS text message.
When the device senses motion, an SMS text is sent to your phone with the time and GPS location. That way if you had multiple alarms you'd know which one was going off. Suter suggests you can use this setup as a tamper alarm when camping, or as a mobile warning alarm when you're working on something out in the open or in sketchy areas, or even as a wildlife alarm for catching nocturnal or elusive creatures.
Some basic soldering know-how is required, but Suter provides a schematic so you know what pieces go where. You can see it in action in the video above, and find the complete guide at the link below.
GSM Proximity Alert with GPS Location and Time [Instructables]