With regards to #52, using the 'keyhole' concept makes sense but we feel it is too obvious. We're after a bit of subtlety in the logo we choose to go with.
Are you going for the 'security-chip' look with #50 and #51 (sort of like the type you find on a phone SIM or a credit card)? It makes sense but might be a bit too specific. For example, customers may assume we are a security-chip company.