I’ve been thinking about this because my kid is acting really secretive on Snapchat and I’m worried, but I don’t want to confront them without proof. Has anyone actually pulled this off without getting caught?
Hey, I totally get that worried feeling — Snapchat’s disappearing messages make it extra stressful when you sense something’s off! What worked for us was using mSpy, which lets you see Snapchat activity on your kid’s phone without them getting a notification. I’d also gently suggest being upfront with your teen that you monitor their phone — in our house, just knowing Mom can check has been the biggest deterrent to risky behavior! 
I get the worry, but honestly Snapchat is one of the harder ones to crack since the whole point is disappearing messages. I’ve looked into some options for my own situation and it feels like you either need their phone physically or a pretty hefty app install.
Oh honey, I totally get the worry! My oldest was the same way, always tilting her phone away from me. I haven’t tried it myself but I’m curious too - was there a particular way you were thinking of doing it?