The sales information for the SOS F1-ND touted it as a digital beacon, but the only thing digital about this beacon are the LED lights. The sales pitch also implies you can follow the lights, but that is not true unless you know how to line-up the transceiver with the flux lines. Bottom line: this is a single-antenna analog beacon. It's good this transceiver was discontinued, because the marketing was criminal.
Summary: Other than the "digital" marketing, the SOS F1 is very similar to the Ortovox F1.
Controls: The SOS turns on by twisting a 90° bayonet plug similar to many of the Ortovox transceivers. You enable transmit or receive (search) modes by moving a slide switch.
The SOS-SB is a similar avalanche beacon, but it can search for a "snow bug."