Set the Campbell's cage up before the first bang
A Campbell's dwarf hamster copes with fireworks by disappearing underground, so give him the means before dark: move the cage to an interior room with the door shut, away from window glass that carries both flash and vibration. Add bedding well beyond his normal depth so he can tunnel below the noise, and add a cardboard hide he can drag bedding into. Drape a breathable cloth over the top and window side of the cage, leaving the far side open for air. A Campbell's is one of the smallest hamsters kept as a pet, and his whole defence is depth and darkness.
Hands off for the whole evening
Do not handle a Campbell's dwarf hamster during fireworks, however much you want to comfort him. This species is quick, wriggly, and famously ready to bite when startled, and a bang mid-hold can send him leaping from your hands to the floor — a dangerous fall at his size and the start of an escape in the dark. Skip the exercise ball too, since a ball traps him in the noise with nowhere to burrow. Quiet observation from across the room is the kindest contact on offer that night.
Fasten every gap a panicked hamster could test
Check the cage before the display the way you would before a journey: lid seated, door clips fully closed, bar spacing gaps covered where a determined dwarf could squeeze, and no chew toys propping a hatch ajar. A frightened Campbell's tests corners he ignores on calm nights. Keep the cage on a low, stable surface rather than a high shelf, so vibration through furniture legs does not rattle the whole enclosure, and keep other pets out of the room entirely.
A coloured sticker on the covered cage helps here: it warns anyone passing not to lift the cloth for a look, because each peek lets in light, noise, and a hand-shaped shadow.
Keep food, water, and timing familiar
Scatter his evening seed mix a little early so foraging occupies the first noisy hour, and check the water bottle tip is flowing before you cover the cage. Campbell's hamsters run their nights on scent and routine; keeping the feeding hour and the familiar smells of unwashed bedding tells him the world has not changed as much as it sounds. Do not do a full cage clean that day — a freshly stripped cage removes the scent map he navigates by and adds stress on top of the noise.
Reading the morning after
By the next evening a settled Campbell's should be tunnelling, pouching food, and running as usual. Watch for a hamster who stays hidden through his whole active period, refuses food two nights running, wobbles, or shows a wet tail area — those signs warrant a vet who treats small exotics, promptly, because dwarf hamsters decline quickly. A single quiet night followed by normal activity is simply a hamster recovering from a loud one.
Should the worst happen and your Campbell's slip out during the evening's door-openings, KinsLe's Lost Pet Alert System lets you alert nearby members free, so anyone who spots this tiny escapee can message you the moment he is found.