Mice are a frustrating and problematic infestation. They are hard to find and even harder to catch. They usually enter on the ground floor often through a back door that has been left open. They will then rapidly populate your home and begin moving up the walls to the second floor and all the way into the attic. Mice are dangerous and toxic rodents. They sleep in nests that are full of feces and rotting uneaten food. They are not clean like many people perceive them as from television and film. They are a serious health problem. They can cause food poising and worse when they eat your food and can defecate in places you may not realize. Their urine is also dangerous and they cause a prevailing smell to fill the house. This situation can be serious for anyone with respiratory issues like Ashma and in poor areas it can be difficult if not impossible to get rid of them. Mice can also enter through many different kinds of openings from the outside of your house. Weep vents, no matter how tight can be squeezed through and wall vents are like a castle gate to a mouse. Plumbing vents and even foundation gaps with cracks and openings as small as a quarter can be entered. It is very important that if you are worried you have mice to do an inspection of the outside of your house for openings. Sealing holes in the house is a bad idea and will result in more damage as the mice chew more holes. Mice are also dangerous in that they chew incessantly. Like are rodents their incisors continue to grow throughout their life. This allows them to chew on almost anything from wood and drywall to concrete. They can do serious damage to electrical wiring and start a fire in hard-to-reach places like the attic or inside of a wall.
Finding signs of mice is simple enough. Check every cupboard in your kitchen for feces. You can track their movement by the dander they leave and if you listen very carefully, possibly holding your ear to a tumbler against the wall you may even hear the faint rustling of their feet and teeth destroying your home. Hearing this sound is difficult on its own, trying to figure out what it is is harder. Rats are not much louder than mice and squirrels are very good at keeping quiet when they need to.
If you are hearing sounds the best option is to call a professional to do an inspection. If they find anything they can quote on-site for treatment and even do it that day. You can always try to resolve it yourself but be careful what you use. Domestic grade poison is often not strong enough for a serious infestation and snap traps would need to be laid out by the hundreds to make a difference. A professional will have commercial poison and can get rid of your infestation in as little as a month.