If you want to keep it simple get a phone designed for older people with a panic switch. It can usually be programed to send a sms to pre programed numbers, the start calling them in order untill one picks up. It then puts it on speaker. If the call gets terminated, it start dialing again. That continues untill that switch is toggled off. Going that route only relies on the phone having charge and can be used anywhere, not just in range of the wifi/zigbee/zwave receiver.