The B737 NG have 2 sepparate proximity down sensors on each gear downlock link. System1 & 2
System 1, gets power from the ground service bus.
Indication is displayed above the gear lever on the P2 panel.
System 2, Gets power from the Dc switched Hot Battery bus. And are displayed on the P5 Overhead panel.
Dual sensors, Dual circuits eleminate the need for down lock viewers.