.....What I need is a speed alarm, not necessarily associated with a POI.
Is this possible with GPS units?
I really don't want to buy a "speed alarm" and thought I could jump on board with this technology...
After thinking about this a bit, a speed alarm...hmmmm, that would be nice to have, but I don't recall any GPS unit that will give you that feature, but there may be one out there that I am not aware of.
It wouldn't be difficult to implement the alarm part of that, since a GPS will know your speed already. The hard part would be to tell the GPS the speed limit for the road you are on. Speed limits are usually static most of the time, but they may change the speed limit on a temporary basis, like based on time of day, or because of construction, and then you will be in trouble. You don't want to spend time keying in the speed limit as you are driving down the road. Also, if you are driving under heavy tree cover, or in a city with lots of tall buildings, you may lose the GPS signal.
I remember in the old days when cruise control was just coming out, some cars will have a speedo dial with a hand like on a alarm clock. You set it to the speed limit, and if you exceed it, a little annoying beep will go off. But here again, the driver will have to keep on changing that little arm to match the local speed limit.
I think your best options is to work on your wife's lead foot, but it is going to be hard work, I know.