Proximity
If you are of the older generation, you may not prioritise having you mobile phone within reach all the time. In this case a personal medical alarm bracelet of pendant may be best for you. Similarly, if you are not familiar with using a mobile phone then a pendant or bracelet system would be best.
However, with a growing percentage of the population for whom their mobile phone as part of their everyday life, a mobile phone based medical emergency alarm is becoming more practical and cost effective.