An Ohio judge has ruled that data from a pacemaker can be used in court.
Defendant Ross Compton, who faces aggravated arson charges, claims he was woken by a fire at home, packed a case, broke a window and threw out the bag.
A cardiologist told police his explanation was "highly improbable" based on his heart rate and cardiac rhythms at the time.
Mr Compton's lawyer said allowing pacemaker evidence expanded government snooping into private data.
"We take the strong position that medical data regarding the inner functions of one's body, designed to assist a doctor in keeping a patient alive, should be safeguarded against government overreach," he told tech news website CNet.
"As was argued to the court, what is next on this slippery slope as technology advances?"
The fire, which caused $400,000 (£309,000) in damages, broke out in September last year.
According to local paper Journal News, Judge Charles Pater said: "There is a lot of other information about things that may characterise the inside of my body that I would much prefer to keep private rather than how my heart is beating. It is just not that big of a deal."