FIL  turned 90  last summer.   And like everyone up there in years,  showing signs of mental degradation.
So,  last Saturday Eve,   I get a call from  MIL-  'haven't seen  Earl for  a couple hours'..   Could you  hunt him down??

Sitting there,  I'm thinking 'where do I even start'..  We  gave him another hour to show up.  Thankfully,  he never left the place.   
he  shot a  possum and took him out to dispose of the varmint  out in the pasture, and stopped to visit with the neighbor..  and walked in the door just seconds after that phone call.
MIL's memory is part to blame too.  
it's not going to get any better.  
I see there's   cell-based  vehicle trackers,  GPS  trackers,  and several feature options such as;  panic button, geo fencing alerts,  voice-thru capabilities.  
Some use a monthly subscription-  GPS style,  and some tap into your cell phone data plan.  
I'm wondering about  finding one that could be hid,   so  there's no way it would be fiddled with.. maybe even hard wired  so it's 'on'  or at least charging when the vehicle is running.   
Looks like there's a lot to choose from out there.   Anybody have any experience with or recommendations?