It doesn't really matter if you're a no-good, cheating scumbag or simply married to a paranoiac nutcase—either way, you probably don't want your partner scanning your every text message. The iTrust honeypot app can catch iPhone meddlers red-fingered.
iTrust takes a screenshot of your homescreen (which you can take by pressing Sleep+Home at any time) and sets it as a full-screen background. If someone tries to use your phone while it's running, they'll see what looks like a regular homescreen, but won't be able to do anything with it—it's a dead image, after all. Whatever they try to do, though, is saved in an excruciating, slo-mo simulated screen recording.
Intruders could obviously just hit the Home button to kill the app completely (not before trying to tap the screen a few times, though!) and the app doesn't let you recording snooping beyond generalized icon-mashing, but hey! At least you've got proof that your spouse tried to open your call history six times while you were taking a dump, which will surely be of help next time you're having a pleasant conversation abut how much you hate each other and want to die.
A dollar! [iTrust]