Even where reception is bad your phone can sometimes be "pinged" to locate you. As long as it is left on. Turn off the ringer but not the phone.
You'd be surprised how many phones are actually "live" and listening for 'pings' when turned completely off, so long as the battery is still in it (some also require the sim card, if applicable). The amount of power needed to keep those circuits on is negligible and the battery can go for weeks without being seriously affected.
Last year, we had a lost Alzheimer's patient in the area, that was found via cell phone location. As it turns out, his phone had been turned off the entire time.
A few conversations with relatives in the local Sheriff's department revealed that most new phones (post 2003-2005) have those circuits live as long as the battery is in the phone and has even a very low charge. When I bought my last phone, I asked the store manager about the same topic. He verified that pretty much every phone in his store had the 'ping' function live as long as the battery was in the phone.