You decide. The device has up to 10 contacts that it can communicate with. You can change these contacts anytime you need to.To program the device, change settings and turn features on and off by sending simple SMS(text) messages to the device using your own cell phone.Yes. Your nominated contacts be can easily changed by sending it a message with a new contact numberSend a simple SMS (text) message to the device and you will receive a return SMS with the devices location with link to google mapsAnyone can call the cell phone number of the device and chat to the user with in-built speaker and microphone. The device will answer automatically.