Keyless entry is a mechanism on a key ring fob that sends a signal to a car or house to lock or unlock it. It uses radio transmission to send a unique signal to a receiver located in the system it was designed to activate.
Some keyless entry systems do not require physical activation. If the device containing such a system gets close enough to the house, car or building to which it is coded, the lock can open automatically. Usually, the activation codes are set up by the device manufacturer, but there are models where the customer can program the device.