NB-IoT has three power saving features:

PSM (Power Saving Mode): Puts radio module into sleep mode to save power. When a power saving feature is active, it is not possible to initiate a downlink connection from the server to the device. It can only be woken up by a timer or own sensors. Upon wake-up, since the data session (PDP context) stays valid, no energy is needed to re-register (re-attach) the device at the network. Long Periodic TAU (LP-TAU): Extends the standard sleeping interval by setting a long TAU (Tracking Area Update) period. eDRX: Useful if frequent paging (“listening”) is required. By switching off the receive section of the radio module for few seconds or more, the UE is able to save power. Whilst not providing the same levels of power reduction as PSM, eDRX may provide a good compromise between device reachability and power consumption.