I carry a cell phone, and if I am going in deep, my 5W 6-meter/2-meter/70cm Icom Amateur Radio HT.
Niether of those devices work particularly well more than a few miles from civilization. The HT is limited by a lack of local listeners, but gets anywhere from 1 to 50 miles of transmission range, depending on local conditions, further if a repeater is installed within a few miles. The Cell is useless for calls most places, but it does work for text messages where voice fails (they use different transmission methods), and can in some circumstances (esp. if you have a 1-channel GPS in the phone), be used to locate you.
The BEST emergency com devices are shortwave amateur radio transceivers, and sat phones, because they allow for two-way communications. If you don't have a ham license, or can't afford a sat phone, some PLBs are priced in the realm of possibility. I would never buy a sat phone, PLB, or other sat device unless I was going somewhere stupidly remote, or if I was operating a boat or airplane, because they are expensive, and false alarms are much more expensive.
The best system in my mind is redundancy. A buddy, a compass and a map AND a GPS, a whistle and a mirror and a glowstick or flashlight, AND leaving where you are going with a third party who isn't hiking with you, for BOTH buddies. Technology can and will fail you at the worst moment. I never hike anywhere deeper than two miles or so alone on trails, and a half-mile alone bushwhacking, anywhere that isn't heavily travelled...ANYM
ORE. Somewhere on this forum are my laments about my two solo Eagle Creek Bushwhack attempts. That went well...
