my friend tried this before, she changed to 密码锁. She used the excuse of there is burglary around the area and change the code every 2 weeks ..
old people hates to remember codes all the time.. so after a while, her in-law gave up on coming to her place.
at the start will be a little tough to remember to keep changing code, but after her in-law stop coming to her place.. she doesn't have to keep changing the number anymore.