16: Magical Devices
19: Visual Trigger (Magical)
17: Phantasmal Killer
Trigger: Visual (Magical)
Save: Intelligence Check
Reset: Automatic Reset
Special Effects: None
Duration: Instant/1d6+6 Rounds
Bypass: Sheath All Blades/Destroy Trigger
This trap is situated in a room that once served as the bedroom of an illusionist (or someone served by an illusionist, at your option). If you have an illusionist that fits this trap for your campaign, use that character; otherwise, you may have the illusionist be some long-forgotten anonymous NPC or you may want to fully develop the illusionist as an NPC in your game.
Whatever the case, this illusionist was afraid of assassination and set a magical eye in the wall to watch for drawn blades. When this eye sees blades of any sort, it casts Phantasmal Killer upon whichever characters are bearing drawn blades.
The spell Phantasmal Killer is found on page 112 of OSRIC. It's an illusion, but an illusion that will scare its victim to death if it's not disbelieved with an intelligence check and if it succeeds in hitting the victim. It will dissipate after as many rounds as the level the spell is cast at. If you don't know the level Phantasmal Killer is being cast at, roll 1d6+6.
Every entrance to this room is a door with carvings on it. The carvings should, in some way, with whatever level of subtlety you think is appropriate or entertaining, signal that characters should sheath their blades.
One possible carving is a simple exhortation to sheathe blades in a language that the party members may or may not know, or in magical writing, requiring an expenditure of a Read Magic spell to read.
Another possibility is a relief showing figures entering the room. In one panel the figures enter with weapons drawn and a fearsome beast attacks them, slaying them. In a second panel the figures enter without weapons drawn and they are unharmed.
The key is to have some sort of warning on the door for the players. The warning may be obvious and clear or somewhat convoluted, requiring effort, time and/or resources the players may or may not be willing to have their characters expend. It should be obvious to the players that there is media on the door; whether they choose to examine it or not is, of course, their choice.
The magic eye inside the room should also be obvious. Personally, I would have it be a stylized eye in a relief on the wall. The eye is obviously deeper than the rest of the relief and, at your option, glows. The relief should be some scene that the illusionist would find enjoyable or comforting, such as an achievement, promotion or victory of his or perhaps a central scene from his religion's teaching. Smashing the eye to pieces will disarm the trap and cause any active Phantasmal Killers to dissipate. Note that the trap only activates when the magic eye sees a blade; other weapons (such as a club to smash the eye) may be brandished with impunity. It is your option whether sharp points count as blades or not.