Abstract: Security systems and methods control access at remote locations protected by electronic locks. Users open or otherwise manipulate an electronic lock via an electronic key device. The electronic key device may be an open architecture PDA programmed to function as an electronic key device, while retaining its general-purpose PDA functionality. Alternatively, the electronic key device may be a special-purpose device designed to function as an electronic key device. The key device and the lock box communicate with each other, preferably, by infrared techniques. The lock box and the key device are administered by a central authority via a central computer, which coordinates all security measures through the use of, e.g., frequent updates; tokens that the key device cannot read; checksums, including Message Authentication Codes; and encryption. A plurality of key devices may be programmed to open the same lock box. A key device may open a plurality of lock boxes.