RFSense is a low power feature of the EFR32 Wireless MCU family. It can "wake up" an MCU from its EM2 or even EM4 power modes. Practically, it is an ultra low power interrupt source, running on ULFRCO clock.
The RFSense is a wide band circuit, it can detect energy in the 100MHz - 5 GHz frequency range, filtered only by the matching network of the RF front end. This is an advantage, as no need for separate PCB components. But it’s also a drawback: it is sensitive to any kind of interferer signal as well.
EFR32xG22 has an updated RFSense module, which improves the performance compared to EFR32 Series 1 in multiple ways:
In legacy mode, EFR32xG22 RFSense is fully compatible with the one in Series 1. This means that if the RFSense module detected energy for a configured time, it generates an interrupt.
Selective mode mitigates the unfiltered nature of RFSense. Instead of simply detecting energy for a given time period, it detects "a pattern of energy", which is essentially an OOK packet. The packet is Manchester coded, uses fixed 1kbps bitrate, 1B preamble and 1-4B sync word (no payload added). This packet can be transmitted by any OOK capable device, including all EFR32 wireless MCUs (Series 1 and Series 2).
Selective mode offers 2 configuration options to select from: "optimized for sensitivity" or "optimized for noisy environment".
For more details on selective mode, see AN1244: EFR32 migration guide for Proprietary applications