The OKY3439 reed switch is a 5VDC, 18x15x4.44mm sensor manufactured by OKYSTAR. It is a small, contact-based sensor typically used for providing alerts of open or closed positions in various types of equipment. This reed switch utilizes magnetic fields to detect its open or closed statuses, with a voltage range of 5VDC. The outer dimensions of the reed switch are 18x15x4.44mm. This sensor is produced by OKYSTAR, a manufacturing company based in China.