A bearded dragon runs its whole day on external heat, using a hot basking spot to digest, move and stay alert, so losing power removes the engine of its routine. A healthy adult tolerates a temporary cool spell better than many owners fear, and the real dangers in an outage are panicked overheating from improvised heaters, feeding a cold dragon, and an animal slipping out while the vivarium stands open in a dark, busy room.
Slow the cooling and warm one end only
Cover the vivarium with blankets or foam insulation on the outside, keeping vents clear, and close the room's curtains and door to hold whatever warmth the house still has. Place wrapped bottles of warm water or activated hand warmers against the outside of one end, creating a warmer zone the dragon can approach or leave, and never put loose heat packs under the animal or a hot bottle where it can press its belly directly against it. Holding your dragon against your body under a jumper is a reasonable short bridge for a calm adult while you prepare the set-up, but return it to the secured vivarium rather than letting it wander a cold floor. Avoid placing the enclosure in a sunlit window as a substitute heater, since glass can swing temperatures sharply and leave the dragon unable to escape the heat.
No basking heat means no meals
Pause feeding for the duration of the outage, even if your dragon watches you hopefully at its usual salad time, because food eaten without a proper basking warm-up afterwards can sit undigested in a cold gut. Water can stay available in its normal shallow dish, and a dragon that was mid-shed or recently fed is best simply left quiet and insulated. Use a battery-powered thermometer at floor level where the dragon sits, check it at intervals, and note the lowest reading reached, since a night dipping toward the cool temperatures these lizards naturally sleep through is very different from a freezing room. Resist repeated opening of the doors, because each opening dumps the warmth you have trapped.
Restore heat gradually and watch afterwards
When power returns, bring the basking spot back and let the dragon warm itself at its own pace before offering a modest first meal once it is active, gaping slightly under the lamp and moving normally. Confirm the thermostat, lamp and timer are all working as a system, because a surge or a reset timer can leave a lamp blazing at midnight or off at noon. Over the next several days watch for black-bearding that does not lift, lethargy after warmth returns, undigested food, wheezing or mucus, and contact a reptile vet if appetite and alertness do not return with normal temperatures or breathing looks laboured. A dragon that cooled for many hours in a cold house deserves that lower threshold for advice, even if it seems merely quiet.
Keep the dragon accounted for in the dark
Outages bring torches, doors propped for cables and people stepping around the vivarium, so treat security as part of temperature control: doors latched after every check, a headcount after moving anything, and the room door shut so a loose dragon stays findable. If you move your bearded dragon to a travel carrier in the warmest room, choose a ventilated box it cannot push open, line it for grip and keep it off cold floors. Prepare before the next outage with in-date hand warmers, spare thermometer batteries and insulation stored beside the vivarium. If the worst happens and your dragon gets out and beyond the room during a blackout, a free KinsLe Lost Pet Alert System alert reaches nearby members at once and lets a finder message you directly, which matters for an animal that will seek a warm corner and hide.