GPS Handheld with an alarm that will keep beeping
 

This question sounds easy, but so far a solution has been elusive.

I would like a small GPS handheld that has a basic lcd screen, tide tables
and most importantly an anchor alarm that won't stop beeping. I want to use
it as an anchor alarm but I want the alarm to keep beeping until it is
acknowledged.

Garmin tech support tells me that their small marine handhelds, like the GPS
76 will beep once and stop beeping. That won't necessarily wake me up. I
need something that will keep beeping until I hit a key to acknowledge the
alarm.

That seems easy, but apparantly it isn't available in the Garmin handheld
line. Are there any other manufacturers that have a handheld that will keep
beeping??

David