many safe locks used to protect critical infrastructure are tested and certified to resist TEMPEST attacks. These include the Kaba Mas X-10 and S&G 2740B, which are FF-L-2740B compliant. Spiking the lock Low-end electronic fire-safes, such as those used in hotels or for home use, are locked with either a small motor or a solenoid. If the wires running to the device (solenoid or motor) can be accessed, the device can be 'spiked' with a voltage from an external source - typically a 9 volt battery - to open the container. Keypad-based attacks If an electronic lock accepts user input from a keypad, this process can be observed in order to reveal the combination. Common attacks include: Visually observing a user enter the combination (shoulder surfing) Hiding a camera in the room which records the user pressing keys Examining fingerprints left on the keys Placing certain gels, powders, or substances on the keys that can be smudged or transferred between keys when the combination is entered, and observed at a later time. Placing a "skimmer" (akin to those used for credit card fraud) behind the keypad to record the digital signals that are sent to the lock body when the combination is entered. Examining wear or deformity of buttons which are pressed more often than others Many of these techniques require the attacker to tamper with the keypad, wait for the unsuspecting user to enter the combination, and return at a later time to retrieve the information. These techniques are sometimes used by members of intelligence or law enforcement agencies, as they are often effective and surreptitious. High-security keypads Some keypads are designed to inhibit the aforementioned attacks. This is usually accomplished by restricting the viewing angle of the keypad (either by using a mechanical shroud or special buttons), or randomizing the positions of the buttons each time a combination is entered. Some keypads use small LED or LCD displays inside of the buttons to allow the number on each button to change. This allows for randomization of the button positions, which is normally performed each time the keypad is powered on. The buttons usually contain a lenticular screen in front of the display, which inhibits off-axis viewing of the numbers. When properly implemented, these keypads make the "shoulder surfing" attack infeasible, as the combination bears no resemblance to the positions of the keys which are pressed. While these keypads