After a somewhat extensively long conversation with +Douglas Cole last night we got to talking about Danger Sense. His character, the Commander had it and we both forgot it at crucial points. Between the two of us we discovered that's actually fairly common - the other fairly common in-play is the player who constantly abuses it. I like a middle path. Here's a few guidelines I like to use in my campaigns.
Danger, Danger Will Robinson!
Keeping track of Danger Sense and when it might come up is problematic. If you're a heavy computer user for your RPGs (and most folks are now) Microsoft comes equipped with a "Sticky Note" program which I use for everything. Keeping relevant traits on the screen to gander at during play is a smart move. I've even used timers (again, Microsoft is well-equiped here) to remind me to look at the notes just in case.
Another good trick is to keep track of where Danger Sense might show up in your adventure notes and memorize or consult them often.
Danger Sense as Impulse Points
GURPS Power-Ups 5: Impulse Buys (see Serendipitous Guidance, p. 8) allows each level of Serendipity to be give two "Serendipity Points" which can be used for Player Guidance (Impulse Buys, p. 7-9). In Pyramid #3/61: Way of the Warrior the Tactician power-up allows Destiny Points to regenerate faster - but only allow the Destiny Points to work in certain ways. Using that logic Danger Sense no longer functions per RAW, but instead gives 3 "Ambush Points" every game session which can be used for rerolls, player guidance, etc. - but only if the character is surprised in some manner (combat, natural disaster, and so on). To compensate for such a narrow field such points can be used retroactively even after the GM declares a result.
Pay to Play
One of the things about Danger Sense is that it requires the GM and player to always be on point with character traits. In the heat of game play things can be forgotten. What's more, it can really irk the GM to have to backtrack a carefully placed ambush because one player realizes he might have a chance to not be surprised. To save time for such arguments the GM could decide that Danger Sense costs Character Points (or Impulse Points) to use. If so that turns Danger Sense from a 15 point trait to a 3 point trait. The GM could narrow that further down to a perk and say that points can be spent only when dramatically appropriate. That allows combat savvy characters to still detect an ambush, while keeping the GM's head from exploding.
Needs Less Spidey Sense...
Danger Sense isn't less absolute - but with a high enough Perception (or multiple levels of Reliable) it becomes more so. So how to "kick it down a notch?" Add Hypersensory to it. For one sense this is -80%, two is -65%, three is -50%, four is -40%, and -30% for five. For example, if Danger Sense relied on you being able to see the threat this is a -80% limitation.
Needs Moar Spidey Sense...
On the other hand, if you want to make Danger Sense kick in all the time (you brave, brave GM). It's a simple matter of adding "Cosmic, No Die Roll Required, +100%" and possibly Reliable. There are threads...endless threads (said in Morpheus' voice from the Matrix) where Detect (Danger) and Danger Sense are bandied back and forth with forumites trying to figure out which is which and what covers what. That being the case you could probably lift both Precise (you know exactly where the danger is coming from) and Analyzing (you know what the danger is) and use them as is without any modification.
Picking Over the Bones
Danger Sense is one of those prickly traits (like Daredevil, Weirdness Magnet, and many others) that players should ask the GM before taking. It's a part meta-game, part cinematic trait and it's not appropriate for all games. There are definitely people in the world who get the willies when bad stuff is about to go down and since psychic abilities have yet to be proven true I'm willing to call that a hyper-awareness to your environment. As with all things GURPS - if your player takes the trait (and you've let him) let him use the damn thing. No player takes a trait without it meaning to be used and Danger Sense is no different. Be nice to your players. Familiarise yourself with their characters - it's the only way to play.