A serial rapist testified in California that forgetfulness led him to let the power in his ankle monitor run too low twice while he was on supervised release — missteps that prompted prosecutors to seek his return to a mental hospital.

Santa Clara County Judge Richard Loftus heard testimony in the matter and will issue a written ruling involving "pillowcase rapist" Christopher Hubbart later. He has a 90-day deadline to rule.

A contrite and polite Hubbart told the judge Wednesday that keeping the ankle monitor fully powered was his responsibility. Prosecutors say it is a condition of his release.

"I failed in my responsibilities," Hubbart said.

Hubbart, 64, was released from a state run mental hospital in July and placed in a small house in Antelope Valley about 60 miles east of Los Angeles.

He has acknowledged raping at least 40 women between 1971 and 1982. He was declared a sexually violent predator and placed in the mental hospital after his prison term ended in 1996.

Doctors declared him fit to live in the community in 2013.

Six residents of Palmdale and the surrounding area drove 350 miles to attend the Wednesday hearing in San Jose.

"We don't want him in our community," resident Norma Valenti said outside court. "He should be locked up forever."

Valenti is a member of a group that protests each day outside Hubbart's home.

Hubbart's release also has prompted calls from local elected officials for the revocation of his release, and law enforcement officials have said they were concerned about public safety.

Hubbart is required to wear the monitoring device around his ankle, attend therapy, undergo polygraph exams and submit to random searches of his house, where he lives with an around-the-clock security guard.

Hubbart is tall and thin and needed eyeglasses to read documents in court. He has thinning, brown hair and a grey moustache.

Tim Fletcher, a retired police officer in charge of Hubbart's security, said the two violations were the only blemishes on Hubbart's record since his release.

Fletcher said he was not recommending that Hubbart be returned to the mental hospital because others have let batteries run low on monitoring devices.

Hubbart's monitor was out of commission for two minutes in September, though two live-in guards were with him.

Santa Clara County public defender Christopher Yuen declined comment outside court.