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I feel that there are many applications or software with this functionality.
But, usually, it is called and understood as spyware (at least, when it is not used with explicit consent OR not on its own device). So, this is really not recommended state to relationships.
Furthermore, most of available such applications or software (with too "straight" functionality) can be too tricky and potentially dangerous. What about something more official: encryption is used more often already - thus - some old school things like (direct access) are not suitable anymore. Another one are something between "spyware" and things like DLP.
Perhaps, web with a lot of articles about subject (even with your "query"). And solution is pinned to your certain setting: location, abilities, device type, OS and so.
But, maybe, more good to spend more time with him (just). I think it is interesting to trick him... but more interesting to be together forever.