Per 
Item #: SCP-4456-SL
Object Class: Keter
Special Containment Procedures: Each instance of SCP-4456-SL is to be stored in a supercooled containment chamber, at least 15m long and 10m wide, fitted with infrared cameras. Placed in each chamber is to be a random assortment of doorways, hatches, locked containers, and other objects for SCP-4456-SL to "guard". At random intervals, automated drones are to be released into the chamber to attempt to access whatever SCP-4456-SL is currently guarding. Destroyed drones are to be removed and disposed of every two days, conducted by D-Class personnel who are informed to not attempt interaction with anything within the chamber other than the drones. Should SCP-4456-SL perceive a retrieval subject as a threat, they are to be considered lost.
Site-19 currently houses SCP-4456-SL-01 and SCP-4456-SL-03. Site-02 currently houses SCP-4456-SL-02.
Description: Instances of SCP-4456-SL are autonomous, bizarrely-shaped organisms composed of angular plates of galvanized steel in a vaguely-defined, symmetrical form. These plates are always unpainted, and float with no apparent support in varying patterns. SCP-4456-SL instances hover roughly one foot off the ground, and are always exactly six feet tall from top to bottom. SCP-4456-SL instances are completely silent, and have been documented moving at speeds of up to 36 km/h.
Testing on steel shavings obtained from SCP-4456-SL reveal that it is anomalously resilient to conventional damage and immune to heat in excess of 4000 K. Temperatures below 70 K do not appear to affect the steel in any way, but when SCP-4456-SL is exposed to these temperatures, its movements slow dramatically, and occasionally halt completely.
When uncontained, SCP-4456-SL exhibits behavior similar to a trained guard dog. It will choose, apparently at random, an interior space, an entryway such as a door or hatch, or, in some cases, a person, and through unknown means, fade from the visible spectrum of light. Observation through infrared viewing has shown that SCP-4456-SL will "guard" a chosen location in this state, remaining fully motionless. After a certain stimulus occurs (typically opening a door, though this varies case-by-case), SCP-4456-SL will become active, revealing itself and approaching the offending creature in an attempt to kill it.
When provoked, SCP-4456-SL uses its limbs, which taper to sharp points, as weapons in order to dispatch anything it views as a threat. Against human beings, SCP-4456-SL prefers to attack from behind by impaling one of its limbs through the top of the head and through the neck, typically resulting in an instant death. Should a target become aware of SCP-4456-SL and avoid this attack, it generally uses its limbs as slashing weapons, albeit to much less effect. In the majority of cases, SCP-4456-SL will return to its previous position, but at times, SCP-4456-SL will pursue the threat for varying lengths of time.
If contained within a small area or otherwise restrained, SCP-4456-SL becomes extremely violent. Through blunt force, SCP-4456-SL will attempt to escape confinement at all hours of the day with no pause, and is capable of damaging materials such as concrete and cast iron in a short timespan. For this reason, containment of SCP-4456-SL is centralized around stimulating it rather than restraining it. SCP-4456-SL instances do not appear intelligent, but if a guarded area provides too little traffic, they will attempt to move onto a new one, and will exhibit these destructive behaviors if it does not find a new place to guard in its current room.
It is highly suspected that uncontained instances of SCP-4456-SL exist in the world, due to the difficulty of tracking them and sporadic nature of their behaviors. While there are no hints to the origins of SCP-4456-SL instances, some plates have revealed serial numbers, QR codes, or other identifying marks. In all but one case, these marks are unintelligible or otherwise make no sense. The sole exception is a QR code, which, when decoded, reads "PROPERTY OF THE FACTORY | BEHAVIOR MAY BECOME ERRATIC OUTSIDE OF DESIGNATED AREA | PLEASE RETURN IF FOUND."
