The Siemens 3RH1122-1KN40-0LA4 is a SIRIUS auxiliary contactor in the S00 frame size — the smallest footprint in the SIRIUS contactor family, at 45 mm wide, 57.5 mm tall, and 72 mm deep. It carries 2 normally-open and 2 normally-closed instantaneous contacts, rated at 250 V, with a built-in varistor surge suppressor across the DC coil. The coil draws 11 W on closing and holds at 4 W.
The contact ratings vary significantly with voltage, which is typical for DC switching. At 24 V the contacts handle 10 A; at 110 V they drop to 1 A; at 220 V it's 0.27 A. For AC loads the picture is different: at 230 V it's 6 A, at 400 V it's 3 A, at 500 V it's 2 A, and at 690 V it's 1 A. If you're switching milliamps, this contactor won't give you headaches.
Keep it inside the enclosure, not on the panel door.
Screw terminals accept 2x 0.5–1.5 mm², 2x 0.75–2.5 mm², or 2x 4 mm² solid conductors. That covers most control wiring up to 4 mm² — enough for the coil supply and contact wiring. The S00 size (45 mm wide) is the standard auxiliary contactor footprint; it shares the same DIN-rail pitch as the main SIRIUS contactors in the same frame size, so it stacks cleanly next to a 3RT2 contactor. Shock resistance is 10g for 5 ms and 5g for 10 ms — fine for industrial cabinet mounting on a machine base.