You can use hand warmers which are fairly inexpensive and can hold heat up to 8 hours. They can be found in the sporting section of Walmart or any sporting goods store.
Just make sure you put a cloth or towel between your beardie and the hand warmer.
I just set Swordtail's timer for his bath and paused it so I could actually fill his soaking bowl up and he crawled over my phone and canceled the timer
Mirage came out of brumation on April 26. He was doing great. On May 2 he started acting funny. We just redid his tank, and he keeps going into one of his hides. He just lays there. He shows no intrest in food. HELP!