Some bottle warmers have a light that goes off when the bottle has reached temperature; others have an audio alarm in case you are in another room. Many also have a “keep warm” setting to keep the bottle at temperature until you’re able to get it.Be wary of models that have no alarm or auto shut-off feature of any kind. You’ll have to do the timing yourself and keep a close eye on the bottle, which can be tough if you’re exhausted and taking care of a newborn.