I am currently using two nRF24L01+ (2.4 GHz RF transceivers) together with two AVRs to create a keyless entry system. My problem is battery lifetime when using a CR2032 battery to power the key.
The key will sleep until a signal is received from the other unit, then wake up and respond.
The RF modules have a power-down mode in which they consume about 900 nA which would be ideal. The problem is that when the module is sleeping it won't listen for any signal and therefore won't send the necessary IRQ to wake up the AVR.
If I put the module in Standby-mode it might trigger the IRQ, but unfortunately it consumes about 26 µA which is to much.
Is there any RF receiver capable of listening for a message and sending an IRQ while consuming <10µA? The data rate doesn't really matter since it could be used only to wake up the AVR, and let the nRF do the rest. Range should be at least 3m (9 ft).
Perhaps someone has some inside knowledge of how car manufacturers have solved this?