The Siemens 3SF5811-0AA08 is an AS-Interface emergency-stop slave with a red mushroom pushbutton actuator and a yellow plastic enclosure. It carries both EMERGENCY-STOP and EMERGENCY OFF functions, with positive opening contacts — meaning the NC contacts are mechanically forced open when the button is pressed, even if they've welded shut. That's the safety-relevant feature that lets this part sit in a Category 0 or Category 1 stop circuit per IEC 60204-1. It's an F slave with 2 inputs (2I), so it reports its state over the AS-i bus without needing a separate safety relay in the cabinet — the safety PLC or AS-i safety monitor handles the logic. The rotate-to-unlatch mechanism means you twist the mushroom head to reset it; no key required.
The housing is designed for floor mounting (vertical orientation) and uses a standard 22 mm panel cutout — round hole, plastic enclosure front is square. The unit ships pre-wired on a strip terminal, so you're not crimping AS-i flat cable connectors in the field; just strip and terminate. Dimensions are 85 mm wide, 85 mm high, 64 mm deep — compact enough for a shallow enclosure lid or a small junction box.
Substance prohibitance date of 05/28/2009 references the RoHS compliance cutoff — the part meets RoHS requirements as of that date. No separate UL or CSA listing appears in the spec record, but the AS-i compliance and positive-opening safety contacts are the governing standards for machine safety circuits.
The DC rated voltage is 30 V — that's the AS-Interface bus voltage, not a separate control supply. The slave draws its power and communication from the AS-i yellow cable, so no additional 24 VDC wiring is needed. One AS-i slave address consumed per unit.