Vibration Sensor Pad

A thin, adhesive pad placed against a floor, wall, or window, detecting the vibration of footsteps, a forced door, or a break-in attempt and silently relaying an alert to the user long before anyone is close enough to be seen or heard directly.

Its sensitivity has to be tuned carefully for its surroundings, since a busy street or a building's own settling can trigger a false alert if it's set too fine.