Arson investigators have been called in to investigate a suspicious fire at an apartment complex on the city’s Southwest Side early Wednesday morning, San Antonio police said.

Firefighters responded around 4:30 a.m. to the apartment complex in the 7100 block of New Laredo Highway after receiving reports of a ringing alarm.

Firefighters said it appears someone set fire to a Halloween decoration hanging on the door of a third-floor apartment.

Authorities say the fire never went beyond the door, but it did set off the sprinkler system and the building alarm, alerting residents.

The sprinkler system dumped water onto the concrete landing outside the apartments but very little got inside anyone’s home, firefighters said.

There were no reported injuries.