I support our physical access system. We have a policy that badges must be displayed and used individually for access (no "piggybacking"). Lost cards are deactivated on notification (and are automatically placed in a "never use again" table in the system), and the employee/contractor is issued a new badge. I'm not sure of the cost of prox cards since the business manages that portion ;^).

In reality of course, real people 1) forget their badges; 2) enter a building/floor en masse by piggyback (try asking 25 senior management types to swipe individually on their way to a meeting); 3) don't display their badges; 4) let other people in on their card; 5) etc. We can only set policy and design/manage the system to our best expectations.

I wear my badge on a reel on my belt. It's always handy, and besides my tinfoil-hat wallet wouldn't allow it to be read.