[vicky_molokh]

Q: How does Detect handle target-rich environments? Does it need Selective Effect to be prepared for them?
A: Here's some discussion that should shed some light on the question:

Originally Posted by Kromm

That's just a logical side effect of Analyzing, actually. The Cosmic included there means that IQ rolls for detailed analysis never fail, so you can instantly sort through all sources and know exactly what you've detected.

Originally Posted by Kromm

Sure he can. But now he has to roll vs. IQ for analysis – a simple Per roll for detection isn't enough. The point of Analyzing is that you don't have to attempt this roll . . . it's automatic. Adding Cosmic means that you don't even have to roll if the GM deems the necessary task to be "detailed analysis" rather than mere "analysis," which seems likely for "everybody in creation" but not for "everybody within tens of yards." The goal of my build in the quoted post was to anticipate all likely GM-imposed obstacles to be as over-the-top as possible.

Originally Posted by the_matrix_walker

I may have confused matters by bringing up that particular post.

Over the top examples aside, I'm trying to determine if unmodified Detect can look past known sources, or narrow it's search parameters.

Can the guy with Detect Humans look past his buddies and find someone lurking in the woods?

Can someone with Detect Metal attempt to look specifically for gold?

Does the use of Detect (actually detect all sources in range, but then) need a successful analysis roll to perform these feats?

And if not, is Selective Effect the way to do those things?

Thanks again.

Originally Posted by Kromm

Basically, Detect can detect any subset within its purview – that's why broader forms of Detect cost more, not less. What allows this to work is not excluding a known source or specifying a subset before the search starts, but making the IQ roll for analysis afterward. The simplest way for the GM to handle this is to make the Per roll, look up the margin on the Size and Speed/Range Table to find the range, and then have an IQ roll assess the nature of any appropriate targets within that radius. The better the IQ roll, the more specific the details.

I don't see how Selective Effect really fits . . . That's for active area-effect abilities, while Detect is really no more such an ability than is hearing or smell. Just as abilities with the Discriminatory modifier can't have Selective Effect, I'd say Detect cannot by virtue of making Analyzing available.

Originally Posted by the_matrix_walker

So Detect can in fact pick up things other than the single closest significant source of what you are detecting? The Advantage listing doesn't really read like that... It reads more like you can detect the closest thing that will set it off, and then you can make an IQ roll to analyze that (and nothing beyond it). So that if, by example, there is a pound of gold buried 20 feet from a 2 ton vein of iron, Detect Metal (by the reading in the Basic Set) would never find the gold, as the iron trumps it, and analysis only works on what you actually find.

If I'm reading your response correctly, Detect finds all instances of your subject in sense range, and then analysis (be it by IQ roll or automatically with Analyzing) sorts all that out?

Originally Posted by Kromm

I think the existing wording makes for a lousy ability, to be honest. It also leads to stupid arguments . . . "Sure, you can use Detect (Metal) just as soon as you take off all your armor."

That is correct. Honestly, would you pay 30 points for Detect (All Life) so that you can confirm that you have skin bacteria? Even with an "exclude known sources" clause, a jerk GM could have you detecting a mosquito on your helmet, a worm 10 cm from your boot, etc. I think the interpretation I gave is a lot fairer to players.

Q: Do Reflexive sensory abilities (primarily Detect) suffer a -4 when activated reflexively on their sense rolls?
A:

Originally Posted by Kromm

The roll at -4 is the activation roll. A Sense roll isn't an activation roll . . . what Reflexive does here is count as a level of Reduced Time (so you don't need actions to use your senses, like a Concentrate maneuver to attempt a Vision roll to spot a distant target) and let the sense wake you up. I agree that the distinction between activation and use rolls in GURPS leaves something to be desired, but they are different.