State public safety officials have overhauled security alarm regulations in a move that independent security installers say will protect the public from unscrupulous subcontractors.

Since Jan. 1, all employees of companies that are licensed to install security systems have had to undergo a criminal background check performed by their employers, and employers have had their backgrounds checked by the state Department of Public Safety.

In addition, the public safety agency has tightened up license rules by requiring local wiring inspectors to obtain from anyone seeking a permit for security system work to present either their special security "S-license," or a certificate of background clearance at the time of permit application.

The changes were announced in a Nov. 22 letter to municipal wiring inspectors from Todd M. Grossman, deputy general counsel for the DPS.

They are meant to update and clarify rules that have been in effect since 1988 but have not been enforced, said Thomas G. Gatzunis, the state commissioner of public safety.

"It's something that's been on the books that we should have been doing all along, but because of misinterpretation has not been done correctly," Mr. Gatzunis said.

For example, while S-license holders have been subject to CORI (Criminal Offender Record Information) checks, employees such as salesmen, installers, data entry clerks and others have not.

Now that they are, homeowners and business owners can be more confident that electricians and security company workers who are coming into their homes, handling sensitive computer data such as passwords and user names, or monitoring video surveillance systems have been safely vetted, those in the industry say.

"This is extremely good news for businesses and extremely good news for consumers," said James Colleary, acting wire inspector in Southboro and a security-licensed master electrician. "It makes reputable companies stay reputable, and it makes those that aren't come up to standard."

Two major industry groups, the Massachusetts Systems Contractors Association and the Massachusetts-Rhode Island Wiring Inspectors Association, have endorsed the new rules.

The contractors group, which has a membership of about 300 companies, has worked with the DPS to review the rules.