A sand timer, also known as an hourglass, is a device used to measure time. It consists of two glass bulbs connected by a narrow neck, allowing sand to flow from the upper bulb to the lower one. The amount of sand and the size of the neck determine how long the timer runs, typically ranging from a few seconds to several hours. Sand timers have been used for centuries in various cultures. They are often used in games, cooking, and even in some scientific applications. Unlike modern clocks, sand timers do not require batteries or electricity, making them a simple and reliable way to track time.