Sure you can go in. If someone gets a residential security alarm system and it is set up to call 911, they would expect you to invesigate their home. A door ajar would indicate that a burglary is taking place and/or the homeowner is in trouble. If you enter to clear the residence, just make sure to continue yelling "Metro Police we have an alarm" and only look where a person could hide. As you go through the residence you will quickly know if a burglary has occurred. If everything looks in order,