The third design consideration is security. Clearly, bullet resistance is of little use if the truck's operators and cargo are not securely separated from the outside world. With this in mind, security measures are aimed at installing and maintaining barriers. Most armored cars operate with two armed guards—a driver, who never leaves the vehicle, and a second guard known as a hopper, who rides in the cargo hold and carries valuables to and from the truck. The driver's compartment is separated from the cargo area by a steel bulkhead. The doors through which the hopper travels are fitted with slam locks, which automatically lock when the door swings shut. Once these doors are locked, the driver must reopen them electronically from the inside. Inside the cargo area, the hopper may place valuables inside a locked box, or he may use a drop safe, which has a one way chute and can only be opened once the truck has returned to its home facility. The gun ports installed in each door employ a spring-loaded plate that must be slid open from the inside to prevent assailants from using them to fire into the vehicle. The security requirements necessitate additional steps to accomplish the final design goal—crew comfort. [links]