Hi Betsy, first off is the alarm wire's hole chalked all around (it should have been)? What I'd suggest is to do a complete inspection on that entire wall's exterior. Check to see that the trim around the window is chalked, check the siding above and around the window, check roofing shingles above that area for missing shingles, inspect the weep holes in the bottom of the window sill, etc. If your siding is the type that runs vertically (non-lap) inspect the seams every 4 feet (horizontally) to be sure it's chalked. The type of chalking you'll need is an exterior "paintable" chalk, the price of which will vary depending on the number of years listed on the label.
When chalking (i.e., around the window trim) run a bead where the trim meets the siding, then go back over it with your finger to create a seal between the two surfaces. Have a wet rag handy to wipe the excess off your fingers. The chalk needs to cure at least one day before doing any painting.
Ooops, forgot one thing... when checking the siding also check any trim boards that might be running horizontally about 8 feet up. These are covering the seam where the sheets of siding meet and should be chalked too.