This is a professional watch and it is important to note that it is not designed for leisure use. The built in micro transmitter broadcasts on the 121.5 MHz aircraft emergency frequency. If a pilot is to crash land an airplane, he is able to activate the micro transmitter which will alert search and rescue. The micro transmitter is activated by removing a cap on the watch which releases an antenna. The distress frequency has a range of approximately 100 miles and transmits on the frequency that is monitored by Cospas-Sarsat, an international search-and-rescue operation. The rescue signal will remain operational for 48 hours.