Meh; the type of signal does not matter. Until all of cell phone/GPS/Wifi-geolocation coverage is actually 100%, including inside of every building, down in every valley, and inside of every tunnel, there can be no expectation of continuous signal.
Meanwhile, being on call 24/7, 365.25 (this includes every fucking weekend, and every fucking holiday, and every fucking vacation -- no matter how remote) is a recipe for employees (me) finding ways to avoid it.
Realistically, I usually left the phone out of the Faraday bag: Mine had two compartments, one shielded and one not, and I used it as a continuous-duty cell-phone case. When I decided it was *my* time, I put the phone into the shielded side, and I'd periodically check for messages.
I really didn't care about what my boss thought of where I went, or how fast I got there on my own time (he got a speed alert on his own phone one day. His jovial SMS response: "134MPH. Niiiiice!").
It was more a matter of: If I want to take time off and go down in the holler in Kentucky, get drunk, eat lots of bacon and shoot guns, then I'm NOT going to be working, nor am I going to continuously cater to a cell phone. (And yes, I always let them know in advance when I'd be leaving for such a jaunt.)
A better solution is to have rotating on-call duty, with allowance for being absolutely-goddamn-away-from-work, and turning off tracking when one is absolutely-goddamn-away-from-work. Despite being a 9-5 shop supporting 24/7 systems, we had plenty of qualified techs to make things work, and it was an unreasonable expectation that all of them be absolutely on call at all times.
Especially for hourly employees with no stake in the company.
Meanwhile, leaving my phone on my desk would be such a slap in the face that I wouldn't have a job when I came back from Kentucky, and there would be no way for me to help during the time that I was gone if my counterparts really needed me.