What repels mice immediately?

There is no repellent that reliably repels mice immediately and permanently on its own, but certain strong deterrents can cause mice to avoid a specific area for a short time when combined with cleaning and trapping. The most immediate physical deterrents are strong smells that irritate their sensitive noses, such as peppermint oil, cloves, ammonia, and vinegar, applied to cotton balls placed near entry points, though the effect fades quickly within a day or two and mice habituate. The presence of a cat or the sound of a cat can cause immediate avoidance of open areas, but many mice learn to avoid the cat rather than leave the house. Bright lights and loud noises may cause mice to freeze or retreat temporarily, but they will return when it is quiet and dark. Electronic ultrasonic repellers claim immediate repelling, but scientific studies show limited and short-term effectiveness. What actually provides immediate reduction is not a smell but mechanical action, setting multiple snap traps or electronic traps baited with peanut butter along walls where droppings are found, sealing entry holes with steel wool and caulk to block reentry, and removing food sources so mice must travel further and are more likely to encounter traps. For true immediate relief from many mice, a professional pest control inspection with aggressive trapping and exclusion is the fastest method.