Victims of crimes, including those alleging rape, are to be asked to hand their phones over to police - or risk prosecutions not going ahead.
Consent forms asking for permission to access information including emails, messages and photographs have been rolled out in England and Wales.
It comes after a number of rape and serious sexual assault cases collapsed after crucial evidence emerged.
Victim Support said the move could stop victims coming forward.
But police and prosecutors say the forms are an attempt to plug a gap in the law which says complainants and witnesses cannot be forced to disclose relevant content from phones, laptops, tablets or smart watches.
Director of Public Prosecutions Max Hill said such digital information would only be looked at where it forms a "reasonable" line of inquiry, with only relevant material going before a court if it meets stringent rules.
The digital consent forms can be used for complainants in any criminal investigations but are most likely to be used in rape and sexual assault cases, where complainants often know the suspect and there may be crucial evidence in their communication before or after the alleged incident.
The forms state that victims will be given the chance to explain why they don't want to give consent for police to access data.
But they are also told: "If you refuse permission for the police to investigate, or for the prosecution to disclose material which would enable the defendant to have a fair trial then it may not be possible for the investigation or prosecution to continue."