It's called E-MiLi, which stands for Energy-Minimizing Idle Listening.

ENGADGET: New 'subconscious mode' could improve smartphone battery life, supress your WiFi id

E-MiLi can also be used with other wireless communication protocols that require idle listening, such as ZigBee.

ENGADGET: New 'subconscious mode' could improve smartphone battery life, supress your WiFi id