The device called Axon is made by Taser International. It's the size of a Bluetooth earpiece and officers say it's surprisingly light.
"I would hit this one the P goes off and a red light shows up here that I can see. Now I am in live recording mode, so I am recording audio and video right now," said William Doane from San Jose Police.
The camera is always on record and when the officer hits start, the last 30 seconds of stored video and everything after will be recorded on this device, worn on an officer's waist.
"And that is Y-video of what is coming through my camera right now. So you're recording us. I am recording us right now," said Doane.
The video collected cannot be erased by the officer and is downloaded at the police station.
This makes San Jose the first major city in the United States to use this technology. The police department says it will be a big help when collecting evidence.
But the department has been investigated for excessive force in some cases.
San Jose resident Andrew Martinez hopes the cameras will bring transparency
"I hope there will be more justice and more checks and balances to keep the police department to be able to do their job correctly," he said.
"And if an officer did something wrong, we want to know that too," said Chief Robert Davis from San Jose Police.
Others say police will feel intimidated.
"I would feel less secure because the police would be holding back because they are being caught on tape," said San Jose resident Akshay Alaghatta.
Police will use it for three months and will then evaluate the results. Because it's a pilot program, San Jose PD pays nothing.