My latest attempt involves simple carbon dioxide. I drilled a hole in a bucket, attached a tube and filled it will dry ice and some water. The tube was inserted into an active hole and then covered up. Hopefully, it will live up to its word and be a silent killer. I put hot water in it at first and didn't close the lid because of the pressure. I love dry ice bombs, but that wasn't my goal. Plus, we don't want to wake up in the middle of the night to a terrorist attack.
After it died down a bit, I put the lid on tighter, but not all the way. Since it's going to be cold tonight, it will sublimate slowly and the little devils won't wake up from their final slumber.