How did Batman keep his Batcave secret from the citizens of Gotham City? He had one of these bad boys installed near the Batcave driveway. Grab a driveway infrared wireless alarm for $36 from Ifocus International Ltd.

Specifications:

• When a person or vehicle, etc. passes the sensor (transmitter), the receiver emits an audible tone to notify you. 
• Use to monitor your driveway or mailbox - an animal or a doorway - or use it to monitor a child's room or the pool gate.
• Battery operated, 400 foot range (line of sight; less range through walls, etc). 
• Sensor range is five metres, which covers most driveways and paths. 
• No wiring is necessary.
• Requires one 9V and 2 AA batteries (not included).
• For optimal performance, please install the detector and receiver above three feet off the ground.
• Keep the detector and receiver in sheltered places to avoid contact of both units from water and direct sunlight.