Product review (3 stars): Not a magnet
That's the first thing I noticed after unwrapping it - it's not a magnet.  OK, I should have read the description more closely.  The adhesive backing works fine and I'm sure won't be any issue in the future.

However, the slide action on this alert is a little snug and not very smooth going.  If you buy this, you can pop out the slider, take a utility blade and very GENTLY shave some off the sides so it moves back and forth easier.

For its basic intended purpose, it's TOTALLY fine.  But not much more.