I use this guy, not sure who made it. It just snaps on under the carrying handle and you never know its there until you DON'T HAVE TO CHASE BRASS IN THE SNOW.
I got it in the late 70s and it still works today.
Takes as instant to snap on and off, faster then installing an Empty Chamber Indicator (which I'm quite fond of).
Like I said, I don't know who made it, a while back this topic came up and I found it doing a google search so its still out there.