We had Phillips Lifeline for my mom. Had the additional fall detection feature added. She only took it off when she got a shower, but had help for showers so she wasn't alone. It was connected through the phone line and if you fell or pushed the button someone would come on to see if you were ok. Unfortunately, her hearing was not good so if she was in another room she really couldn't hear the person talking to her. My sister and I were both the contact people if they couldn't reach my mother. We also had a lock box on the front door if anyone needed immediate access before we could get there.
I recall it costing $50 a month but that was about 2 years ago. We were not charged for the equipment and when she was done using it we sent it back. There was also no contract to sign. Which is the reason I didn't go with Lifeline, I felt that there were a lot of hidden cost with them. Make sure you research whoever you decide to use and ask lots of questions.