The invention provides a closure system comprising an obstacle detection system for detecting objects in or near the path of a moving closure. The system comprises a remote module, a remote module timer, and a communication unit. The system further comprises a motor to drive the closure between open and closed positions, a controller for controlling operation of the motor, and a base station coupled to the controller for communication with the remote module and to transmit synchronization signals at first prescribed intervals. The remote module is arranged to have at least three modes of power usage: an operation mode, a standby mode, and a sleep mode. The system is further arranged such that, when in sleep mode, the remote module is configured to switch for a preset duration to said standby mode at or substantially at said first prescribed intervals to detect said synchronization signals so as to monitor the communications link between the base station and the remote module.