Fitbit data has been used by US police investigating whether a 90-year-old murdered his stepdaughter.
The victim, Karen Navarra, 67, was found with a kitchen knife in her hand, suggesting she killed herself.
Anthony Aiello, who denies murder, told police he had visited her for 15 minutes to drop off pizza.
But police say a fitness tracker she was wearing showed a significant spike in heart rate followed by a rapid slowdown at the time he was there.
Mr Aiello was arrested in San Jose, California, in September and is due in court later on Thursday.
According to a police statement obtained by USA Today, Ms Navarra's Fitbit Alta device showed a raised heart rate at about 15:20 local time, when video evidence suggested Mr Aiello's car was at her house.
It then recorded her heart rate slowing rapidly and stopping at 15:28, five minutes before he left.
It is not the first time Fitbit data has been used in a murder case.
Last year in the US, Richard Dabate was charged with murdering his wife after data from her Fitbit discredited his version of events, according to police.
Mr Dabate had said he had seen his wife, Connie, shot by an intruder more than an hour before her fitness tracker had recorded her last movements, they said.
He pleaded not guilty and is awaiting trial.