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.
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.