[Analemma_]

I can sort of see that as a concern, but... why on earth would you wear your Fitbit to a police interview? If I ever got hauled in for questioning by the cops, then guilty or innocent I would definitely not be wearing something that tracks my heart rate!

In any case, I don't think this would be admissible evidence. As far as admissible evidence, polygraphs are only just scraping by on the skin of their teeth, and wearable devices don't come close to their level of accuracy/depth. The main reason these devices can be sold with none of the regulation that accompanies "real" medical equipment is that the companies state up front that "to be used for general fitness only, not intended for use to treat any particular disease", etc., and their accuracy reflects that. The heart rate measurements of Fitbits and other wearables aren't awful, but they're sufficiently inaccurate that any decent lawyer should be able to get that thrown out without question. Edit: Not to mention JTsummers' point about there being no baseline/control measurement on this data, if it existed. Definitely not admissible.

If you want something to be worried about vis-à-vis wearables and the privacy of health data, worry about your health insurer getting a hold of it and jacking up your premiums for not taking enough steps every day. That, to me, is the real worry here, not the cops.

[animal531]

But perhaps you were wearing it while murdering your neighbour. By itself it should be circumstantial evidence at best, but it could possibly help pointing the police in the right direction.