In simple terms, to be classified as a Class M-compliant MOB, your device must be fitted with a GNSS positioning device and, most importantly, a transceiver operating on VHF DSC channel 70.
The DSC receiver allows vessels that have detected your alarm to acknowledge it. This feature enables remote deactivation of your MOB device, either in the event of a false alarm or after your alarm has been activated to let the user know their signal has been received. This stops further DSC transmission, although the MOB will continue to broadcast the unit’s location coordinates via AIS.