In this technique all devices listen for a periodic beacon from which slots are timed
and then listen in their assigned slot for a message. The amount of slots and the
amount of listening is dependent on the network size and required response times.
The frequency of listening for beacons depends on the super-frame size and the clock
drift. The listening for beacons and slot messages needs to begin early enough to
allow for any clock drift. Listening in a slot needs only continue for as long as
necessary to confirm that no message is being sent this time. The beacon period and
resulting frequency of listening is a trade-off between power consumption and
system responsiveness.
This technique involves searching for preamble with a duty cycle of listening less than
100% of the time, e.g. 50% of the time or 25% of the time, this reduces power
somewhat but it is still a relatively power hungry technique. When preamble is
detected the receiver switches to full powered RX mode to receive the frame. To talk
to a device employing sniff mode the transmitter needs to send a longer preamble
than would otherwise be the case to give the receiver a chance to detect it and
receive the frame.
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