MCouple, developed by US surveillance firm mSpy, offers a GPS tracker, contacts viewing, Facebook message reader and SMS and phone tracker.
Couple Tracker, the 79p app which has had up to five million downloads, sells itself as "the best affair and cheating prevention and detection mobile application".
Its features include GPS-tracking every half hour, full call history and a statistical overview of everyone commenting and liking their partner's Facebook posts.
Relate counsellor Christine Northam said if both sides want it, the app can be beneficial.
"If, on the other hand, it is a 'need' in a relationship, someone thinking 'I must know where exactly my partner is', then I would question why."
- Daily Mail