Cambridge police are asking residents to be on alert following a series of house break-ins. Since mid-October, police have seen similar break-ins near Broadway and Harvard streets, police said in a monthly crime report. Burglars have entered homes mostly through open side windows between 8 and 11 p.m. In Cambridgeport, police saw five reported break-ins near Putnam Avenue and Allston Street in the first week of October. Police are investigating these robberies separately from other home break-ins, police spokesman Dan Riviello said. There were about 20 break-ins in later September, most in first-floor apartments around the 1500 to 1800 block of Massachusetts Avenue, between Harvard and Porter squares, police said in a statement. In most cases, entry was gained through an unlocked window between 7 and 11 p.m. Residents who would like Cambridge police to assess how safe their home is can call 617-349-3236.