Most toilets in china are still squat-toilets. Therefore, phones and wallets won't survive in your pocket, you have to hold it or put it somewhere. The problem is, when a box is built to hold these stuff for you, people often left them in and the items were often stolen by the subsequent users of the toilet. 

Slab lock combines a slab for your items with the lock, so you will never leave anything behind. A functional prototype was built in my school where this was a huge problem, feedbacks were very positive.