Abstract: A shopping cart security system assists in preventing the theft of a shopping cart from a parking lot of an establishment where the carts are used. The parking lot has at least one entrance and exit driveway. The system includes a magnet mounted on the shopping cart and an actuator buried below the surface of the driveway for generating a signal in response to passage of the cart with the magnet over the driveway. The actuator extends generally transversely with respect to and substantially completely across the driveway. An alarm issues a warning in response to the signal generated by the actuator. Also, a system for monitoring unauthorized entry into a restricted area having a door, a magnet carried by the door and an actuator controlled by the magnet for signalling opening of the door.