A security alarm went off Saturday at a Fulton County warehouse containing ballots from the presidential election, prompting private security guards hired by election skeptics to enter an unlocked door and investigate.

The incident led to a mass email from the most vocal critic of Georgia’s election, former President Donald Trump, who called for greater ballot protection.

Ballots remained secure within a locked area of the building that has its own secondary alarm system, according to county officials. It’s unclear what triggered the motion sensor alarm located upstairs in the warehouse, in a separate area from where ballots are stored. The security guards didn’t find anyone inside.

The false alarm occurred as plaintiffs in a lawsuit are seeking to inspect 147,000 absentee ballots for counterfeits after Democrat Joe Biden defeated Trump in the state by about 12,000 votes.

Election officials have repeatedly said there’s no sign of significant fraud after three ballot counts and an audit of voter signatures on absentee ballot envelopes, but that hasn’t stopped Trump and his followers from continuing to claim that the election was stolen.

An attorney for the plaintiffs, Bob Cheeley, said Tuesday that he hired security officers to watch the warehouse after a judge last month allowed a future ballot review. Fulton is seeking to dismiss the case.

Fulton sheriff’s deputies left their patrol of the warehouse Saturday afternoon when their shift ended, before the alarm went off, Cheeley said. The front door was probably left unlocked by county employees during the long holiday weekend, he said.

“I’m really concerned about their lackadaisical attitude toward security, particularly leaving the building unlocked,” Cheeley said. “Obviously, Fulton County doesn’t take their job responsibility seriously to protect ballots. … Somebody could have walked in there and set the whole place on fire.”

Fulton Sheriff Pat Labat said ballots remained safe, and his office is investigating the incident.

“I am 3,000% confident and understand that the ballots are secure,” Labat said. “There is no question about that.”

Trump criticized the county for failing to secure the warehouse. Custody of ballots stored in the warehouse is the responsibility of the clerk of superior court.

“We must not allow ANYONE to compromise these ballots by leaving the building unsecured,” Trump wrote in an email to supporters Monday. “Republicans and Patriots must protect this site and the Absentee Ballots. The Left talks about election security but they do not practice what they preach because they are afraid of what might be found.”

Cheeley said the county had told the judge it would keep deputies stationed at the warehouse 24 hours a day, and they shouldn’t have left their post. He said his private security guards were off-duty sheriff’s deputies from Douglas County who are allowed to investigate when an alarm goes off.

If the ballot inspection moves forward, Fulton County would scan high-resolution images of absentee ballots and then turn them over to the plaintiffs. Original ballots would remain in government custody.

Superior Court Judge Brian Amero plans to consider motions to dismiss the case later this month.