There's fear around a new sexual consent smartphone app that could be used by sexual predators.

The app, Legal Fling, allows people to choose yes or no to different categories like using condoms or explicit language.

Shine director Jill Proudfoot said she can't imagine the usefulness of it to anyone except sexual predators who want to protect themselves against rape allegations.

She told Chris Lynch two people might sign the app together then the abusive person might spike the other person's drink.

"And then have sexual activity while she wasn't really in the consenting state. That person would still have the evidence that she had consented."

Proudfoot said the app removes the human conversations people need to have and replaces them with pressing a button.

She said predatory people use all sorts of technology abusively, and this is another opportunity for them.

She said consent isn't a one-off decision.

"Someone might consent early in the evening to particular behaviours and then decide they don't want to do that, and then it's forced upon them but the person forcing them has evidence that they have consented."

Proudfoot said the app lends itself to huge dangers.

LISTEN TO JILL PROUDFOOT TALK WITH CHRIS LYNCH ABOVE