Bed sensors are commonly used to detect if someone is out of bed at an unusual hour, for a long period of time and if they are still in bed when they should already be up.
 
Main Features
Mat:30 in. x 11 in. x 0.3 in. (L x W x D) Dark blue, water-resistant, antimicrobial nylon cloth RF-sealed with black, water-resistant, slip-resistant, polyester cloth
Cable:Gray, 18in, 26 AWG, 4 conductor sheathed, terminated with RJ9 connector
Power:2 AA batteries
Electronic Enclosure:White, 3.5 in. x 2.5 in. x 0.8 in. ABS plastic
Activation Weight:Minimum 50 lb. subject directly above mat
Sensing Interface:Filtered, normally open (i.e. when not occupied), momentary contact switch