By Kent · Lock Depot Staff Writer

SDC 1091 vs 1291: Fail-Safe or Fail-Secure Spacesaver Bolt

Some openings don't have room for a standard electric strike or a maglock bracket. A narrow aluminum elevator lobby door, a shallow storefront frame, a cabinet-style gate at a pharmacy counter: the frame is too thin for the hardware everyone defaults to first. SDC built the Spacesaver mortise bolt lock for exactly that gap. It's an electric bolt that mounts into a slim mortise pocket instead of a full strike box, and it comes in two flavors that get confused constantly: 1091 and 1291.

The names on the box tell you the whole story if you know how to read them. The 1091AIC is the FailSafe version. The 1291AHC is the Failsecure version. That single word is the entire decision, and getting it backwards on a fire-rated egress door is the kind of mistake that fails an inspection or, worse, traps someone on the wrong side of a locked door during an alarm.

What fail-safe actually means on this lock

FailSafe means the bolt releases when power is cut, whether that's a deliberate signal from the fire alarm panel, a building-wide power outage, or someone pulling the plug. SDC's own listing calls the 1091 out as being on the California State Fire Marshal's list for locking perimeter and emergency exit doors after hours, specifically because it fails open on a power loss and never leaves an exit path locked when the building loses power or the fire system trips. Inside the lock, large repelling magnets sit in the bolt and strike; if the return spring itself fails mechanically, the magnets still eject the bolt and release the door. That's a second layer of redundancy most electric bolts don't bother with.

Failsecure runs the opposite direction. The 1291 needs power applied to release the bolt; cut the power and it stays locked. That's the correct choice for a door you want locked during an outage rather than automatically open. Think a server room, a narcotics cabinet door, or any opening where losing power should not mean losing security. Do not put a failsecure bolt on a required means of egress unless your fire marshal has explicitly signed off on the configuration; on most exit paths, code wants fail-safe.

The hardware is otherwise identical

Strip away the fail mode and the two bolts share the same body. Both carry an 8" x 1-1/2" x 1/8" faceplate, a 4" x 1.5" x 1-9/16" strike, and a 5/8" nylon bolt with a center magnet. Both fit a minimum 1-3/4" face frame, which is the actual reason to reach for a Spacesaver instead of a standard electric strike on a narrow opening. Both run on a dual-voltage coil rated 0.45A at 24VDC or 0.9A at 12VDC continuous duty, and both include an adjustable auto-relock switch and a pair of aluminum mounting tabs for a straightforward retrofit into an existing mortise pocket.

Both series also come in a version with a door position sensor, a bolt position sensor, or both, for a monitored opening that reports status back to an access-control panel. If you're wiring this into a system that expects supervision, order the DBD (door and bolt position) variant up front rather than trying to retrofit a sensor into a bolt that wasn't built for one.

Getting the choice wrong is not a small mistake

I've seen a failsecure bolt get specified on an egress door because it was cheaper by a few dollars and nobody caught the function code on the submittal. It passed the punch walk because nobody powered down the building during the inspection. It failed six months later during an actual outage, when a corridor that was supposed to fail open stayed locked. Read the part number before you order, not after it's installed. AIC/AID/AIG/AIH/AIP/AIQ/AIV/AIY suffixes on a 1091 all denote FailSafe in different finishes; AHC/AHD/AHG/AHH/AHP/AHQ/AHV/AHY on a 1291 all denote Failsecure. The finish letter changes; the function letter block does not.

Ordering the right sensor configuration

Beyond the base FailSafe or Failsecure bolt, both series offer a door position sensor alone, a bolt position sensor alone, or both together. If your access-control panel is only checking whether the door is closed, the door-position-only version is enough. If the panel also needs to confirm the bolt itself actually extended, not just that the door is shut, order the version with bolt position sensing. Skipping the sensor you need means a second truck roll and a return shipment later, so confirm what your integrator's panel is actually monitoring before the PO goes out, not after the lock is already mortised into the frame.

Common questions

Which one do I need for a fire-rated egress door?

In almost every case, FailSafe (the 1091). Code generally requires an exit path to unlock on a fire alarm signal or a power failure. Confirm with your local fire marshal or life-safety consultant before you order, since local code can vary.

Can I retrofit this into an existing mortise pocket?

Yes, that's the entire design intent. The Spacesaver bolt fits a minimum 1-3/4" face frame and mounts with the included aluminum tabs, which is why it exists for openings too narrow for a standard strike.

What's the difference between the AIC and AICD suffixes?

The D adds a door position sensor for monitored status reporting to an access-control panel. Order it if your system expects supervision on that opening; skip it for a simple standalone lock/unlock function.

Does this work on 12V or 24V systems?

Both. The coil is dual-voltage: 0.45A at 24VDC or 0.9A at 12VDC, continuous duty, so it matches whatever power supply is already feeding the rest of your access-control hardware.

What happens if the return spring fails on the FailSafe version?

Repelling magnets built into the bolt and strike still eject the bolt and release the door even if the spring itself fails mechanically. It's a second layer of redundancy on top of the spring, not a substitute for maintaining the hardware.

Both bolts are in stock in bright brass and several other finishes. Browse the rest of the electrified lockset lineup on the SDC hub, and see our write-up on the SDC Z7800 for another fail-safe-versus-fail-secure decision on a fire-rated stairwell door.