Detecting Invisible Creatures
Invisible creatures and things are not detectable by normal sight or by
infravision. They do not create any significant distortion or haze pattern that can
be noted. However, invisible creatures aren't completely undetectable. First,
things still cling to them. Flour thrown into the air is useful for this purpose,
although it can be easily covered, washed off, or brushed away. Second, they
do not leave invisible footprints. Again, flour on the floor is a good way to
spot the movement of invisible creatures.
The effects of specific environments are more subtle. Fog and smoke do not
reveal invisible creatures. Smoke and fog are filled with swirls and eddies,
preventing the creature from being detected. Invisible creatures completely
submerged in liquids are also concealed; there is no hollow space or "air bubble'' to
reveal the creature's presence. At the surface, an invisible swimmer may be
noticed by the observant as an unusual distortion of the waves.
Invisible creatures are not automatically silent. An invisible fighter in
plate mail still clanks and rattles as he moves, a dead giveaway to most creatures.
They still have scent, so creatures with keen noses can smell them. Indeed,
blind, or nearly blind, creatures are unaffected by invisibility.
A detect magic shows only the presence of something magical without pinpointing it exactly.
Thus, it cannot be used as a substitute for a detect invisible spell. Furthermore, while an actual light source may be invisible, the light
emanating from it is not. This can reveal the location of an invisible
When the DM thinks there is minor but sufficient cause for a creature to
detect an invisible character, a saving throw vs. spell should be made (secretly if
the DM is checking for a player character). A minor cause might be a strange
odor, small noise, an object that disappeared when it shouldn't have, or a
strange reaction from another person (who has been pushed, kicked, poked, etc., by
the invisible character). Such a saving throw should be allowed for each new
event. A wolf would get a save when it detected a strange scent, then shortly after
when it heard a stick break, and finally a last chance when the character drew
his sword from his scabbard. Furthermore, the acuity of the creature's senses
and its general intelligence can increase or decrease the frequency of checks,
at the DM's discretion.
If the suspicious creature or character rolls a successful saving throw, he
detects some small sign of the invisible foe's presence. He knows its general
location, but not its exact position. He can attack it with a -4 penalty on his
chance to hit. If the check fails, the creature or character is unaware of the
invisible opponent until it does something else that might reveal its presence.
Of course, a revealing action (which could range from an attack to tripping
over a pile of pots) immediately negates the need for a saving throw. In such
cases, the character has a pretty good idea that something is not right and can
take actions to deal with the situation.
Finally, even if an invisible character is suspected, this does not mean the
character will be instantly attacked. The result, especially for less
intelligent creatures, may only be increased caution. Having scented the intruder, the
wolf bristles and growls, protecting its cubs. The rattlesnake will give its
warning rattle. Even the orcs may only circle about warily, alert for an ambush.
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