Three suspicious incidents, two of which involved vandalism, are being investigated by Port St. Lucie police.
The incidents happened within a half hour of each other beginning late Friday night.
In the first case police said someone rang a doorbell at a home in the 300 block of SW Scroll Court and before running off tossed a hunk of concrete that broke a front window.
Less than 20 minutes later someone knocked on a door in the 400 block of SW Dauphin Avenue and then left before it was answered.
About 15 minutes after that there was a knock on a door at residence in the 1000 block of SW Payne Avenue. In that case the person smashed out a front window with a concrete block, police said.
All three incidents happened within a mile and two of them were within .2 miles of each other, police said.
Police are warning residents to be on the lookout and to report any suspicious activity.