Mice love the vertical corners of your house. Sealing these corners is one of the fastest, cheapest ways to stop them from entering. This fix takes 10 minutes per corner.
Start at ground level and follow the trim up to the soffit. Look for gaps where siding meets vertical trim.
Push steel wool into the gap until snug. Insert the foam straw halfway and hold the trigger for 3-4 seconds. Let cure completely before trimming.
Once cured, slice flush with a utility knife. Run a bead of exterior caulk over the trimmed foam to protect from weather.