Youve just settled down in bed and are twenty minutes into Letterman when you hear it: a light scratching overhead, accompanied by a squeak here and a squeal there. You assume that its the wind making strange noises (after all, it is windy tonight!), or perhaps the house is just settling (you do live in an older home, so it would make sense...). Maybe the sounds are just the result of an overactive imagination. You hope!

Of course, you just cant get around the obvious conclusion - you have company. Whether its a bird, a bat, a squirrel, or an entire family of mice, theres something up there. Given that youve had recurrent rodent problems, the latter option is probably the safest bet.

However, how can you be sure what type of animal youre dealing with - assuming that you even have unwelcome visitors at all? Before you can evict them, you need to know who they are.

Above all else, your first step is to inspect your home for signs of mice. Different problems call for different solutions; if your visitors are actually squirrels instead of mice, youll need to develop a different strategy.

When canvassing your home, keep an eye out for these seven telltale signs:

1. Droppings and urine

Mouse droppings resemble a grain of rice; they are approximately the same size, but are black in color. Mice will not generally travel across open spaces, so youre more likely to find droppings along walls, pipes, and beams, as well as in storage areas and next to objects. Urine pillars are less common; they consist of mounds of grease, urine, and dirt. You can also use a blacklight to find individual urine droppings.

2. Chew marks

Look for tooth marks and wood shavings (similar in consistency to sawdust) around doors, baseboards, and cabinets. Marks on food containers can also be a clue that you have company.

3. Grease marks

When traveling alongside pipes, beams, and walls, mice may leave greasy smear marks, as dirt and oil from their fur rubs off onto the surfaces.

4. Tracks

Footprints and tail marks on dirty, dusty, or muddy surfaces can indicate activity. If you suspect that mice have taken up residence in an otherwise impeccably clean area of your house, lay down a sprinkling of talc to catch them in the act.

5. Nests

Mice construct nests of shredded paper and similar debris; check attics, basements, garages, storage areas, closets, and other dark, enclosed places for nests or stolen materials.

6. Sounds

Youre more likely to hear squeaks and squawks at night, when the house is quiet and your guests are active.

7. Sightings

Its not uncommon to see mice during the day; although they are largely nocturnal, they do move about in daylight.

Now that youre certain that youre dealing with mice, its time to start strategizing. Your plan of attack will actually come in three phases: first you need to clean up the messes you found; next, you must trap and release your unwelcome visitors; and finally, youll mouse-proof your house so they cant get back in (and wouldnt want to, even if they could!). Good luck!