The Siemens 3RV1901-1AB1 is a SIRIUS lateral auxiliary switch with screw terminals, providing 1 normally open and 1 normally closed contact for circuit breakers in Size S00 through S3. This is a phased-out product; the official successor is the SIRIUS 3RV2 series.
Lifecycle stage is listed as current, but the product description explicitly states this is a phased-out product with the successor being the SIRIUS 3RV2.
This lateral auxiliary switch mounts onto SIRIUS 3RV circuit breakers in frame sizes S00, S0, S1, S2, and S3. The screw terminals accept the same wiring as the breaker's line/load lugs — no separate DIN-rail footprint needed, it clips directly to the breaker side.