There is a chance he slipped out the front or back door while following you as you went outside (our Rex is apt to follow my wife) if she isn't careful when she's on the floor, follows her like a puppydog.
If you have a heat pad, you could set up one on the floor maybe , and surround it with news paper with a sprinkling of flour on it, if he visits it when you are out , he'll leave behind tell tail tracks.
Could leave several sheets of paper sprinkled with flour about the house and check for tell tail tracks on a regular basis , least if he's still inside and roaming about you'll find out.
Is it possible to put his enclosure on the floor with door open and the lights on and maybe his fav greens and veg in there , if he can access the room and it's easy for him to crawl in , you might come home and find him inside there to greet you.... he will regard it as his territory and if he can he will try to get back into it as it's his safe place. (I know someone this worked with (wasn't beardie though but a pink tongued skink)).
Have you checked under the bad (Rex went missing and we found her curled up under our double bed .... after spending hours looking everywhere we could think off. Our Rex squeezes into very tight spaces (behind furnature) while exploring (squeezing in on her side !) ....so we have a few scares with her Puff, on the other hand is no trouble, he'll either obsess with Rex, or mozy over to the sunny window and start there until the sun disappears and he'll then mozy over an ask for cuddle (off me) or make it clear he is now ready to back into his enclosure.
A good sign is that you are not smelling anything.