Which device allows people to descend a rope at a controlled speed?

The device that allows individuals to descend a rope at a controlled speed is a descender. Descenders are specifically designed to manage the rate of descent for a person or load, providing safety and control while descending in technical rescue situations. They typically feature a mechanism that can grip the rope, allowing the user to adjust their speed by varying the pressure applied to the device. This feature is critical for maintaining safety during rescue operations where precision in descent is necessary.

In contrast, ascenders are designed for climbing up the rope and do not facilitate controlled descent. Pulleys are used to change the direction of force in a rope system and can aid in lifting or moving loads but do not provide controlled descent capability on their own. Carabiners are important hardware used to connect components in a rescue system but do not have the functionality to control speed during descent. Each of these other devices serves a unique purpose but lacks the specific mechanism needed for controlled descent that a descender provides.