SBC w/ bluetooth, a cell modem, and a gps, build a cheap portable scanner for the automatic detection and reporting credit card skimmers.
Dog harness + computer vision + cellular network. Tracks dog biometrics and object recognition sending SMS notifications.
Take the worry out of renting with a portable security monitor for belongings!
Remote monitoring of deployed field experiment equipment with IR detection and image capture.
Mobile device that can be setup at a location to check wheter unwanted devices like Google Glass enter the area and warns via Twitter.