US Patent 7420461 Caster-lock with dual receivers

A locking system for stopping a shopping cart includes a caster that can be selectively disabled when the cart encounters an electronic barrier. The caster includes a brake that is mounted on the frame of the caster. Also mounted on the frame are two receivers for separately receiving different signals from an electronic barrier. Respective decoders on the frame decipher lock commands in the signals, and a controller selectively activates the brake to prevent further movement of the cart in response to the lock commands. The electronic barrier can include an underground loop antenna and an above-ground RF beacon.