Shane Tusch found out the hard way that Facebook’s suicide prevention tool works — sort of. In fact, what began as a test of the system landed him in mental health facilities for about 70 hours.

Two weeks ago, Tusch, 48, read about Facebook’s suicide prevention program, which locks out users after their friends report their suicidal posts to Facebook. In order to unlock their account, some users can choose to read suicide prevention materials. Tusch, who lives in San Mateo, decided to see how the program worked by posting his frustrations with his bank and plans to possibly hang himself on the Golden Gate Bridge. He didn’t tell his friends or even his wife about his experiment.

“I have decided to take my life in some very public way,” Tusch wrote on his Facebook page on Feb. 25.

No surprise, his friends got worried and someone flagged the post as suicidal to Facebook. That prompted Facebook to lock Tusch out of his account, and on Feb. 26, a person who saw Tusch’s post called the police.

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Tusch, a part-time electrician who is also a community activist, was out biking that day and came home to a parking notice on his car. He went to a San Mateo police station and was asked about his Facebook post. Tusch confirmed that he wrote it, but also said he wasn’t suicidal and did not plan to harm himself or others. He said posting his feelings was his First Amendment right.

According to the police, Tusch failed to mention that his post was an experiment. Police also say he did not make it clear that he was not a danger to himself.

Shortly after the exchange with police, Tusch said, he was handcuffed and placed under mental health watch. He faults Facebook for what happened, adding that the social network should stay out of evaluating whether people are suicidal.

“It should be left to family and friends,” Tusch said. “There’s too many areas for this to be misinterpreted by what people post.”

San Mateo police said Facebook didn’t call them about Tusch, but they did not identify who did.

Tusch later complained to privacy group Consumer Watchdog, which sent a letter to Facebook CEO Mark Zuckerberg, asking him to suspend the suicide prevention program until there are more safeguards against abuse and protections for freedom of speech. Last month, Facebook said it wanted to provide a way for users to help their friends when they see others post worrisome messages.

Facebook said it wants people to have a safe experience on the social network. In reference to Tusch’s situation, the company said, “This appears to have been a hoax and we are glad that nobody was hurt.”

Any person can call the police to report someone they believe to be potentially suicidal. Police can then detain the person up to 72 hours if they deem them dangerous to themselves or others, according to state rules, said Sgt. Steve Casazza of the San Mateo Police Department.

Facebook is rolling out an enhanced version of its suicide prevention program in the United States. The company worked with several suicide prevention groups on the effort, including the National Suicide Prevention Lifeline. When a user asks Facebook to look at a post because it’s worrisome, a team of Facebook employees trained in suicide prevention evaluate the post and determine whether to lock the account or take further action.

“If at least one person uses our resources and says ... I actually feel better as a result of going through this, that’s a win in my book,” said Rob Boyle, a Facebook product manager, on a video about the suicide prevention tool.

Some suicide prevention experts supported Facebook’s efforts. It’s usually not a good idea to joke about killing yourself, they said.

“Any suicide prevention effort will try to save your life,” said Eve Meyer, executive director for San Francisco Suicide Prevention. “What (Tusch) posted clearly indicated that he was somebody who could die very quickly, and that it wasn’t something they could gamble with.”

Others were doubtful that the situation violated Tusch’s First Amendment rights. Peter Scheer, executive director of the First Amendment Coalition, said he’s read about people posting suicide notes on Facebook before killing themselves.

“Facebook is trying as best as it can in an imperfect world to try to provide some sort of safety net here to people who are acting out a suicide threat,” Scheer said. “Although (Facebook) has to be careful in the way they operate this program, I think most people would applaud them for trying something along these lines.”

Ultimately, Facebook’s program did work as designed. When Tusch got home, his account was locked. He and his wife went through a series of questions, ultimately deciding not to talk to a suicide prevention counselor. Then, Tusch received a questionnaire, asking him if the service was helpful.

“I just find it insensitive, to tell you the truth,” Tusch said.

San Francisco Chronicle staff writer Julie Balise contributed to this report.

Wendy Lee is a San Francisco Chronicle staff writer. E-mail: wlee@sfchronicle.com Twitter: @thewendylee