Even when your cases are unlocked, and there is a notice on the case stating that it is unlocked, TSA, may still force it open.
We returned from New York recently, and as we travel on a regular basis to the US, we are aware of the TSA regulations.
After checking in at JFK, I stuck a notice on our cases stating that the cases were unlocked if required.
On arrival at Heathrow, as our cases came down the conveyor belt, I noticed 1 of our cases was damaged.
TSA in the US had forced open the case, inside the case was an apology, when we got our other case, I opened it, and inside was another apology from TSA, although this case had not been forced open.
These are samsonite cases, and are not cheap, I tried to file a claim at Heathrow with United Airlines for the damage to the one case, unfortunately, and I am aware, TSA have the right to open the case.
So, even if you leave your cases open, make sure there is a big enough notice on the outside of the case, stating that it is unlocked.
Driver02