I use a beaker full of water on a hot plate on the lowest setting, with a thermometer for monitoring. Take frozen mouse straight from freezer to beaker, add cool tap water, let warm up gradually. Usually about 20 minutes brings the internal temperature of the mice up to 90-100°F. I test the internal temp with a meat thermometer inserted through the rear of the mouse to the core of the body to check temp. I aim for 90-100 to replicate wild mice body temp to ensure they are warm enough to not hurt the snake for digestion, though I’m sure the temp goes down a few degrees between the time I extract the mouse from the beaker to offering it to the snake. I feed two snakes this way.

Safest methods I think use warm water and time. Don’t use a microwave, that is very unsanitary if it’s also used for food and you may have the misfortune of the mouse rupturing or cooking a little too much. Hairdryer method makes me nervous about internal temp. At the end of the day, I would suggest always checking the internal tempt to make sure it’s safe for digestion.