the power is saved because of the following.
when a sensor is active and it senses movement a red led lights behind tne lens to indicate detection and a transmition is made. When in idle no led lignts up and no signal is sent.
because the panel can poll the devices i assume the devices transmit an ,i,m here still, signal periodically
Re the signal being confirmed at the panel before the device xleeps. It takes around 7 or so activations to trigger sleep mode