I like Anchor Pro. Use 2 cell phones and the program will notify me via Telegram if the alarm
goes off. Can also send a request for an update that will tell me direction and distance to the anchor setting position. Also will show on a map.
Many cell phones time out the GPS
and program so I have found I need to leave the phone
plugged in and open to the page with the app. Only need to pay the $15(?) once for the pro version (to get the cell notification feature) and can load on multiple devices.