Never use hand warmer with chicks! They may release some harmful gas. I used this shipping warmer to keep day old chicks warm in a large box after picked them up 3.5 hours away: https://www.amazon.com/gp/product/B01949J35K
It similar to hand warmer but should be ok to use around animals. NO! They all pilled on top of the warmer and seemed to enjoy it on the way home. After we arrived home, all chicks passed out and I couldn't wake anyone up when toughing them in the next ~5 hours! None of them ever moved and most didn't open their eyes before I went to bed crying! I thought they all died and left them under heating plate just in case. The next morning, everyone was happily running around in the brooder! I never had chicks doing this kind thing before, but I would never use chemical warmer around my chicks again.
It similar to hand warmer but should be ok to use around animals. NO! They all pilled on top of the warmer and seemed to enjoy it on the way home. After we arrived home, all chicks passed out and I couldn't wake anyone up when toughing them in the next ~5 hours! None of them ever moved and most didn't open their eyes before I went to bed crying! I thought they all died and left them under heating plate just in case. The next morning, everyone was happily running around in the brooder! I never had chicks doing this kind thing before, but I would never use chemical warmer around my chicks again.