These optical tilt switches made by SOLICO are great for use in alarms, games, seismic equipment, vending machines, etc. They consist of an IR LED, photo transistor and stainless steel ball all enclosed in a black glass filled polyamide housing. Provides a safe alternative to mercury switches. Has 4 PC leads. LED operates on 1.2VDC. Sold in package of 5. Size about 0.55" long x 0.31" wide x 0.42" tall.