Consumer electronics are inheritly under-powered and have short runtimes at full power. Using an electronic means for rescue, besides a PLB or Satellite Phone is not the best method of trying to be rescued. Radio requires a transmitter and receiver to both be matched up to receive a signal. If you don't have this match, you don't communicate. You need to be on a frequency that is known to be monitored 24/7, or at least monitored in a known regular fashion like a wilderness protocol. You also have to have enough juice in your transmitter to effectively communicate. Otherwise, you'll hear them, and they won't hear you.

Visual communications are better since no electronics are needed between the source and your eyes. Flares and signal mirrors can be detected in peripheral vision, where as radio signals don't have such a benefit of peripheral vision, except at close range.

In a disaster or rescue situation, don't think digital, think analog.