I can speak to this a bit. Some pacers can be programmed to beep in certain situations to indicate things like, low battery. Alternatively you can set some mode

I can speak to this a bit. Some pacers can be programmed to beep in certain situations to indicate things like, low battery. Alternatively you can set some models up so that when a magnet is applied, different programmable actions occur such as, changing the heart beat rythm to indicate what the expected remaining battery life is. There are also "at home" base stations which upload stats to the manufacturer who can call the patient (through the base station) when there are unexpected problems.