What is the best bed alarm for actual exiting of bed?

daddysfavorite, whatever type of alarm system you get, make sure it is one that won't scare the daylights out of Mom when she does get out of bed.

Use a mat on the floor rather than a bed alarm.
If however there is a chance she will try to get up and if she is a fall risk a bed alarm is better than the floor alarm.

We purchased a mat that goes on the floor and has a portable "alarm" type of receiver. We've place the mat alongside of mom's bed, and we carry the receiver; when my mom steps on the mat, the alarm goes off, letting us know mom's on the move! The alarm receiver can later be used as a call button (you can attach it to the headboard or nightstand) should mom become bed bound. We purchased it from Amazon, and I think it was about $125--money well spent! Other things I like about this alarm is that it's portable--you can slip the mat under the bed when not needed, or move it to another room. It also lets you choose the sound of the alarm (we chose the doorbell sound) instead of the usual high pitched screeching noises most alarms make. Good luck!