You don't need a license to use the aircraft band freq's. 121.5 is the international distress freq and governed by line-of-sight. It is monitored by most military and government agencies. Also, passing general aviation and commercial MAY be monitoring. The rules have increased for flying since 9-11 so the number of aircraft monitoring 121.5 has greatly increased.

The small handhelds put out 5 watts of transmission power. I don't know what that means but I've been 4,000' above the ground and talked to ATC from ~30 miles out.

Carrying and charging them can be a real pain.