They make those stick on things. I think Northern Brewer or Midwest has them. Not sure how accurate they are though. I just gently lift them to see how much is left. Usually I just let them run out and it’s surprising every time, sometimes it’s incredibly sad.
Unfortunately, those little sticker thermometer/volume meters are useless in my setup since I also have a chest freezer kegerator setup. I’d have to lift the keg about 4 ft. read it which would disturb too much stuff.
I will lift the kegs to see how full they are if I’m not planning to have one of those beers for a day or so. This way it gives it time to re-settle.
I have smart strips. I agree if you have a keezer these are useless. I have a regular refrigerator. They work OK. The strips are not the full length of the keg. I have mine mounted so the bottom of the strip is as close as possible to the bottom of the keg. When the beer level is in that neighborhood they work OK. I take a wash cloth in a bowl of hot water to the keg. I rub the strip with the warm cloth (wrong it out first) then wait 30 seconds. There is a fuzzy line at the volume level. It is not a sharp line with super contrast. If there is no line you have more beer than the strip can show or less. The last time I checked and got no line the keg kicked on the next pour.
When filling the keg with cold crashed beer the line is very obvious. The line is also obvious when the keg is not in the fridge (when you take a keg to a party).
If you buy them shop around. Prices vary a lot. I got mine for under $5 each.
There is something worse, that being someone else blowing the keg. You get off work, drive home, strip off the accoutrements of the day, and clunk… no beer. The other person got the “awe” moment, you’re left with the wtf moment.
I accept mystery keg blow anticipation as a fact of homebrew life. I have two cures. A lagering freezer better racking. Cold reserves, that can be moved without sucking up yeast.
Low tech - put a post it near each tap and tick off when you pull a beer. Not totally accurate, but you’ll know when you’re close. Might not work with friends though.
I use a white board and tally each pint. For me, an empty keg weighs about 8 pounds. I weigh each one after I fill it and subtract 8…the number I’m left with roughly equals the number of pints in the keg. It’s not exact, but it’s better than flying totally blind.
That’s not a bad idea at all… Weigh the keg empty (note down weight) and weigh it full (note down weight). Then you can always compare and see how much is left… Though it would require pulling the keg out of the kegerator to do so.