An acoustic system, which may be ultrasonic, operates in a power efficient idle mode thereby reducing the power consumption required by high frequency sampling and processing. While in idle mode, an acoustic receiver device operates with an idle sampling rate that is lower than the full sampling rate used during full operational mode, but is capable of receiving a wake-up signal from the associated acoustic transmitter. When the wake-up signal is received, the acoustic receiver switches to full operational mode by increasing the sampling rate and enables full processing. The acoustic system may be used in, e.g., an ultrasonic pointing device, location beacons, in peer-to-peer communications between devices, as well as gesture detection.