But which ELT is used in Boeing 777s? This isn't my area but reading about them is interesting and it seems one can still elect to use a cheaper model that is up to 97% prone for false alarms.
Different types of ELTs are currently in use. There are approximately 170,000 of the older generation 121.5 MHz ELTs in service. Unfortunately, these have proven to be highly ineffective. They have a 97% false alarm rate, activate properly in only 12% of crashes, and provide no identification data. In order to fix this problem 406 MHz ELTs were developed to work specifically with the Cospas-Sarsat system. These ELTs dramatically reduce the false alert impact on SAR resources, have a higher accident survivability success rate, and decrease the time required to reach accident victims by an average of 6 hours.
Presently, most aircraft operators are mandated to carry an ELT and have the option to choose between either a 121.5 MHz ELT or a 406 MHz ELT. The Federal Aviation Administration has studied the issue of mandating carriage of 406 MHz ELTs. The study indicates that 134 extra lives and millions of dollars in SAR resources could be saved per year. The only problem is that 406 MHz ELTs currently cost about $1,500 and 121.5 MHz ELTs cost around $500. It's easy to see one reason for the cost differential when you look at the numbers. However, no one can argue the importance of 406 MHz ELTs and the significant advantages they hold.
NOAA - Search and Rescue Satellite Aided Tracking - Emergency Beacons
Some explanation about beacon searching:
Anatomy of a 406 MHz Rescue using an EPIRB ELT or Personal Locator Beacon | ACR ARTEX
http://www.cap-es.net/NESA%20MAS/Air...c%20Search.ppt
Interesting also:
Artex B406 Boeing Emergency Locator Transmitter | ACR ARTEX