How does Symbol get used? Spotted?

[Gwarok]

Ok, Symbols have always seemed vague to me. You place them on an object to protect but at what point does it go off? Is there any way to have them be detected and disarmed w/o them going off? Also, can they be cast AT someone to immediately bring their power to bear?

Basically if I guard a book with a Symbol of Death, its sitting on an altar 40 feet away. The PC goes up carefully to check it out, at what point does he die? Is there anything that would/could happen to prevent it other than having enough HP to tough it out?

 

[Patryn of Elvenshae]

Ok, Symbols have always seemed vague to me. You place them on an object to protect but at what point does it go off?

It goes off when it's triggered. Specifically, in the case of Symbol of Death:

As a default, a symbol of death is triggered whenever a creature does one or more of the following, as you select: looks at the rune; reads the rune; touches the rune; passes over the rune; or passes through a portal bearing the rune.

Is there any way to have them be detected and disarmed w/o them going off? Also, can they be cast AT someone to immediately bring their power to bear?

Well, a detect magic spell will find it, as can:

Note: Magic traps such as symbol of death are hard to detect and disable. A rogue (only) can use the Search skill to find a symbol of death and Disable Device to thwart it. The DC in each case is 25 + spell level, or 33 for symbol of death.

Note that, if the triggering condition is "trigger when touched or looked at," any attempt to disarm it will set it off.

Basically if I guard a book with a Symbol of Death, its sitting on an altar 40 feet away. The PC goes up carefully to check it out, at what point does he die? Is there anything that would/could happen to prevent it other than having enough HP to tough it out?

What's the trigger condition?