The city Department of Emergency Management is asking for the public’s help in monitoring outdoor warning sirens for vandalism and reporting suspicious activity.

Thieves have broken into the Haleiwa Beach Park siren and stolen batteries three times since April, the city said. Siren batteries have also been stolen at Makaha and Nanakuli beach parks.

The sirens use two to four wet-cell batteries, similar to, but larger than a car battery, a city official said. The city estimated that the thefts cost taxpayers $400 to $600 per siren.

More important, disabling a siren could put the community at risk during the next tsunami or natural disaster, the city said.

The Honolulu Police Department is investigating the thefts. Officials ask that people who see suspicious activity to call police at 911. Any vandalism, damage or missing siren components or sirens should be reported to the Department of Emergency Management at 723-8960.