Dead women can't talk, but their activity trackers can.

A man in the United States has been arrested for the murder of his wife after his testimony was contradicted by an unusual source: her Fitbit, according to media reports.

Richard Dabate told police that a masked intruder broke into his home in Connecticut, tied him up and shot his wife on Dec 23, 2015.

In his account, he sent his two sons to school and left for work. His wife, Connie, left for a fitness class with the Fitbit on her waistband, CNN reported.

Dabate said that he forgot his laptop and went back to the house to get it between 8.45am and 9am.

At home, he heard a noise and went upstairs to investigate. He claimed he saw a tall, stocky man in a camouflage suit and a mask.

Then, he heard his wife come home and shouted for her to run, according to an arrest warrant.

The intruder shot and killed 39-year-old Connie with Dabate's gun, and she was found with two gunshot wounds, one in the back of her head, BBC said.

The revolver used was bought two months earlier by Dabate.

Dabate told investigators that the intruder tied him to a chair and burned him with a torch. He managed to turn the torch on the intruder, who "dropped the torch, put his hands to his face, and ran out", Dabate said.

According to the Fitbit, however, Connie was active up to 10.05am, long after Dabate said she was killed, BBC said.

She clocked 1,217 feet (370m) at home between 9.18am and 10.05am, far more distance than Dabate's account would suggest.

She also posted videos on her Facebook page from her home IP address between 9.40am and 9.46am, after she had supposedly struggled with an intruder and been shot dead.

Dabate later admitted to having an affair and he was expecting a baby with the other woman.

He also attempted to make a life insurance claim for his wife's death for US$475,000 (S$662,000).

According to investigators, Dabate had texted his wife a year before her death saying: "I want a divorce", BBC said.

Dabate was charged this month with murder, tampering with physical evidence and making false statements.

Dabate's lawyer says his client is innocent.