They didn't work for me that way either. Unless that building has an ammo magazine for the LAW to bounce into....
On the other hand I did have my ears ringing for a week or two due to losing my hearing protection one night just before a live fire exercise in Basic Training. Me being too afraid to tell a Drill that I'd screwed up I went and ran a couple hundred rounds through my M-16 with no hearing protection. I remember how badly that hurt and how long my ears rang. That's why when I see this stuff in movies and TV it puts me off totally.
Which takes me back to my first sentence. Never seen it. Doubt I ever will.