The key thing about a signalling mirror is that it can be useful _if someone is searching for you_ (and provided that you have clear sky above you). PLB or sat

The key thing about a signalling mirror is that it can be useful _if someone is searching for you_ (and provided that you have clear sky above you). PLB or satellite messengers will not only let the first responders know where you are (both by transmitting your location via satellite distress signal as well as using 121.5 MHz 'homing signal' in the case of PLBs to help first responders find your exact location), but also trigger the SAR operation rather than waiting for someone to notice you've been gone for too long.