The Vesper WatchMate XB-8000 smartAIS transponder with WiFi and NMEA 2000 gateway has been voted the best black box a boater can buy. Unlike an ordinary AIS which only sends and receives data, smartAIS from Vesper Marine is an active AIS system with smart alarm logic that proactively alerts you when you have potential collision situations. It plots your anchor position and alerts you if your anchor drags.
The free Android and Apple WatchMap app configures and monitors the XB-8000. Anchor watch shows your position relative to your anchor and triggers an external alarm if you drift outside a configured zone. Low energy consumption allows it to work continuously and does not require your phone or tablet to be on.