Lanefan
Victoria Rules
The way I have it, the only way you'd ever be able to summon a demon via casting Detect Magic would be to have your casting interrupted and then hit some very unlikely (and unlucky!) rolls on the surge table.Ugh. No. I would hate trying to cast detect magic on a piece of treasure and TPK the party by summoning a demon. Any game built like this would be fun for a session while I try to figure out how many character sheets I can make my party and I go through in a session, but I would hate to play it as a regular game.
That, and I've tried to make sure the odds of getting a major bad surge are vaguely similar to those of getting a major good surge; with most of the results (and by far the higher odds) being fairly mundane with a very intentional slant toward the humourous.