It's as straightforward as turning on video recording of your hp and keep it sticking out of the back pocket of your jeans as you hang it on the wall hook facing the bed
Better if there's an app to control file size, timer, and activate the video recording in the bkgd.
Only problem is you will also capture yourself in the action
As other bros recommended, it's all for private collection, good enough. Or better still, don't start doing it.
Some FL/ML are cautious enough to drape a towel over the phone or move your phone elsewhere before staring work. Or dim the lights but nowadays phone cams are advanced enough to capture details even in low light condition.