The patients have heart rate monitors with GPS signalers that signal the cryonics company as soon as the patient flatlines. This is just obviously the way things should be and it is regrettable that the market is not yet broad enough for 'obvious' to have been translated into common practice.

See http://www.benbest.com/cryonics/alarms.html:

"For over fifteen years I have been hearing that the kinds of systems cryonicists would want for vital signs alarm systems will be commercially available within a year or two. In that sense, December 2010 is not that much different from 1995, except that the claims are getting louder and more convincing. I should be getting excited, except that over a decade of feeling like the village idiot chasing a wallet on a string has made me very cynical....

Cryonicist Nick Pavlica seemed to be making some progress with his bed alarm, but after extensive testing by me, I still must say that it gives false alarms or does not alarm when it should. At the moment, the best I can say for the product is that it appears to provide a good panic-button system for dialing to a pre-programmed list of phone numbers."