If he has a cell phone, the police can track the phone number to get his location. I would get the non emergency number for his zip code and keep that on file. You can also do the same with the fire department. Other than that, I would try to get your son some assistance in the city where he can call someone closer. There are many suicide hotlines where he can call to talk. Your hands are really limited, but at least he reaches out. That is hopeful.