Check the listing for details. MTS Model Tuning System Vehicle Sensing System w/ Reed Switch + Circuit #502 Kit. Condition: New, Made in United States. Listed at 54.99 USD. Here up for sale is a MTS model tuning system vehicle sensing system with reed switch and circuit, part #502 prewired electronic circuits kit. Contains one reed contact switch, one magnet, with electronic circuit. System is designed to detect the presence of a vehicle and will provide a contact closure that can be used to operate another device such as a crossing gate or garage door opener, etc. Made in USA. These were designed to be used with the MTS voltage regulator #201 and the MTS 9 volt DC transformer #203. Card states that the "voltage regulator not required if this unit is used by itself", but some limiting on the voltage should probably be done to avoid burning something out. Card has some bends and wear, and blister plastic is factory stapled to the card.