Anchor Alarm app that uses NMEA GPS?

[alctel]

Bit of an odd one here

I have my NSS8 MFD replicated to my tablet/phone using the simrad gofree thingy.

I was wondering if there was an app that I could use as an anchor alarm on my phone that uses the external GPS that comes in via NMEA? I've a GS25 so it's a LOT LOT better than the crappy GPS on my phone that randomly loses signal and sounds the alarm. The anchor alarm on the NSS8 is complete crap (can't move anchor position when set, can only drop waypoint on location to measure from) so I don't want to use that either.