This may be one of the reasons why many countries use banknotes of different size in ascending order of value. A British £5 banknote issued by Bank of England is much smaller than a £50 banknote, and therefore can't be used to create a £50 note. Physical security Tamper-evident physical devices are common in sensitive computer installations, for example network cabling is often run down transparent conduit in plain view and switches located in glass-fronted cabinets, where any unusual device attached to the network can easily be seen. Despite the easy availability of miniature key loggers, tamper-evident design is not often used in personal computers. While transparent computer cases and keyboards are common, they are mainly used for the decorative effect rather than security. Many PCs do have a switch to detect opening of the case, and this provides a visual notification when the computer is next turned on that the case has recently been opened. In any case, it has long been possible to complicate the task of tampering with electronic devices by sealing them with tamper-evident tape or sealing wax. Alternatively, radio-controlled alarm-devices (which transmit a silent alarm) can be installed, or cases can be glued shut in such a manner that tampering attempts will distort or fracture the casing. Fire alarms and other emergency switches are typically non-reversible, using a piece of glass which must be broken to activate the alarm. For example, Panic buttons in burglar alarm systems might require a plastic key to reset the switch. In very much the same manner as with fire alarms, many emergency handles and levers, or handles that are not meant to be opened regularly, are enclosed in a thin metal or plastic security seal. The seal is thin, so as not to prevent the handle from being used (in due time), but only to alert maintenance/security personnel that the handle was indeed used. Many times, large sea-going shipping containers have such a metal ring or seal attached to them at the source port. After traveling at sea (and perhaps by land as well), the containers reach their destination, where each container is checked to have the seal properly in place (against a list of doublets - container/seal). In police work, tamper-evident techniques must often be used to guard access to evidence, providing means of storing items and samples in a way which can be used to prove that