My kids gave me a cell phone for emergencies.
I do need to carry it with me, as I have had some incidents where it might have been helpful. One was that I could not get myself up, but I managed to move over to my long handled spade, and pulled myself up hanging onto it. Another time, while my late DH was in the house, I got locked in my greenhouse when the latch on the outside slid into place. My DH was asleep in the house, and did not miss me, so I had to wait until my son came home and came looking for me.
My other safety device is the car key emergency flasher. If anyone were to bother me at night, I would hit that, and the neighbours would know I was having difficulties.