K2-1821SA-A4SW-06 is a surface-mount tact switch (also known as a push button) manufactured by HRO parts that meets the requirements of Restriction of Hazardous Substances (RoHS) regulations. The switch is designed for panel- or board-level mounting, and features a slightly concave four-pin SMD (Surface-Mount Device) body. The switch has a moving plunger element that can be pressed to initiate activation of a circuit. It has a contact rating of 25V and 50mA, and a lifetime of 1 million operations. The switch is suitable for use in a wide range of applications, including tactile feedback buttons for consumer electronics, touchpads, input/output interfaces, alarm systems, and more.