Do some research. I purchased one for my mother when her health became problematic. She used it several times and worked well. The most marketed one is Life Alert but we went with Medical Guardian. It was a better rated company. Do not forget to get a lockbox for your door so the EMTs do not need to break through the door or window. It has code that will let them open the box to get the key. Price was resonable back in 2018. She passed about a year later. It was definitely a good peace-of-mind for me and my brothers who did not live local.
