# Warning
This article is about the property that alerts you to a hostile monster's presence. For the 'warning' that allows you to sense specific monsters, see warned of monster type.
Warning is a property that appears in NetHack and reveals the location of nearby hostile monsters that you cannot see.

Contents

1 Sources
2 Description
3 Strategy

3.1 Warning levels

4 Messages
5 History

5.1 Older messages

6 Variants

6.1 SLASH'EM
6.2 GruntHack
6.3 dNetHack
6.4 FIQHack
6.5 The November NetHack Tournament
6.6 xNetHack
6.7 SpliceHack
6.8 EvilHack
6.9 SlashTHEM

7 References

Sources
Warning can be obtained as an extrinsic by wearing a ring of warning or carrying an artifact that grants warning, i.e. the Orb of Fate or the Master Key of Thievery. It can be gained as an intrinsic by eating a ring of warning, or reaching a particular experience level as certain roles:

XL 7 as a Monk
XL 15 as a Caveman, Healer, Priest, or Wizard

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Per commit f9a3513, the helm of caution is a new item that confers warning while worn.
Description
 The range of warning is indicated by question marks. In comparison, the range of unblind extrinsic telepathy is slightly smaller, and is indicated by flags.
While you possess warning, hostile monsters that are within a ten-tile radius and are at least level 4 will have their location marked with a number from 1 to 5 (1, 2, 3, 4, 5) - in graphical user interfaces using the default tileset, such as the Windows client nethackw, the numbers are replaced with colored question marks that correspond to the above numbers (    ).[1][2][3]
The number used to represent a monster is 1⁄4 of that monster's level - the result is rounded down to the nearest whole, and will go no higher than 5, while 0 is not displayed.  The glyphs displayed are described as an "unknown creature causing you 

<feeling>", where <feeling> is one of concern, anxiety, disquiet, alarm, or dread for warning levels one to five respectively. Warning levels will be chosen at random if you are hallucinating.
Moving near a hiding monster such as a piercer or trapper while possessing warning will cause you to take a second look close by, revealing the monster. Additionally, warning produces messages to alert you when you are standing on ice that is going to melt in under 15 turns.
Note that moving with m towards a warning glyph while blind will still attack in some cases, possibly petrifying you - this is a bug.

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

The bug is fixed in commit 121290c.
Strategy
Warning is a useful property to pair with other means of detecting hostile monsters, such as extrinsic telepathy - though it does not reveal their identity, it functions regardless of whether the monster is mindless or not, allowing it to cover "gaps" in telepathy. 

Warning levels
The following table lists which mindless monsters each warning may represent, assuming that the player already has extrinsic telepathy. As a result of this, the warning can vary - e.g., an ochre jelly can merit a warning number 1 or 2, depending on the dungeon level and your experience level at the time of its generation. Monsters may also shift warning levels after generation through growing up, e.g. via conflict or quaffing a potion of gain level, or losing levels to spells and attacks that drain life.
While not implemented, there is code to handle warning for monsters with a level below four - these would be represented by a 0 and described as causing you "worry".

Warning symbol

Possible monsters when also telepathic

(I, no warning)

bejvvyFFFFFFFMMPZZZZZZZ'''

1, 

bbeeejjjvvvvvvyyEEEEFFMMMMMMMMPPPZZZZZ''''''

2, 

beeejvvvEEEEMMMMPPZZZ''''

3, 

vEEEEMPZZ''''

4, 

Z''''

5, 

'''

Messages
You feel sensitive!
You gained warning through leveling up.
You feel less sensitive!
You lost intrinsic warning through level drain.
The ice seems very soft and slushy.
You have warning and are standing on ice that will melt in under 15 turns.
You feel the ice shift beneath you!
As above, but in under 10 turns.
The ice, is gonna BREAK!
As above, but in under 5 turns; this is a direct quote from The Dead Zone, hence its punctuation.
History
Warning has been present in NetHack since the first public release of Hack included the ring of warning; the current warning system was first implemented in NetHack 3.3.1.
In prior versions, warning displayed messages when a hostile monster was nearby.[4] A ring of warning would additionally flash a single color corresponding to the warning numbers in modern versions - pink corresponds to "1", red to "2", ruby to "3", purple to "4", and black to "5". Messages that were higher in the list took precedence over lower ones. When blinded, no warning messages were displayed; while hallucinating, they are referred to as "mood rings", and the colors were replaced with hallucinatory ones.
No warning messages were displayed if one had been displayed within your last ten actions, unless the new message reflected a higher level of warning than the previous one.
The Palantir of Westernesse, the Elf quest artifact, conferred warning when carried from NetHack 3.1.0 to NetHack 3.3.0; the role and its artifact were made defunct in 3.3.1.

Older messages
Your left/right ring glows <color>!"
You are wearing a ring of warning.
Your rings both glow <color>!
You are wearing two rings of warning.
You feel apprehensive as you sense a <color> flash.
You have intrinsic warning, or warning from an artifact.
Your spider-sense is tingling...
As above while hallucinating.
Variants
Many variants introduce additional sources of warning, usually from quest artifacts.
In most variants that implement the Convict patch, The Iron Ball of Liberation is the Convict quest, and grants warning among other properties when carried.

SLASH'EM
In SLASH'EM, The Candle of Eternal Flame and The Storm Whistle are additional artifacts that grant warning.
The defunct artifacts The One Ring and The Pick of Flandal Steelskin granted warning when carried.

GruntHack
GruntHack implements the unusued code for warning of monsters that are level four and below described above, representing them with 0. Warning is also one of the many object properties that can appear on certain objects.

dNetHack
In dNetHack, the Android and the Madman role gain warning at experience level 15. The Binder spirit Huginn and Muninn passively grants warning.
The Palantir of Westernesse is reintroduced in the Elvish Racial Quest as an artifact source of warning. Other artifacts also grant warning: Grayswandir, The Black Crystal and The Rogue Gear-spirits while carried, The Hat of the Archmagi while worn, and Helping Hand while wielded.
Great Cthulhu is a monster that can be sensed within standard warning distance as "an unknown monster causing you dread", regardless of whether or not you possess the property.

FIQHack
In FIQHack, red dragon scale mail grants warning while worn.

The November NetHack Tournament
In The November NetHack Tournament, the Really Cool Shirt grants warning when worn.

xNetHack
In xNetHack, Itlachiayaque confers warning when carried.

SpliceHack
In SpliceHack, the Cartomancer gains warning at XL 7. Sharur also grants warning when wielded in weapon form.

EvilHack
In EvilHack, the Healer role no longer gains warning at XL 15, instead obtaining sickness resistance. The Infidel role gains warning at XL 15, and all centaurs gain the property at XL 10. Warning is also an object property that some armor and weapons may generate with.
The beholder is hard-coded to always show up as 5 when detected via warning, regardless of its level; it also does not show up via telepathy, making warning all the more vital to detect one before making eye contact and being subjected to potentially-deadly gaze attacks.

SlashTHEM
In SlashTHEM, some other roles can obtain warning through leveling up - the Zookeeper role starts with warning, the Officer role gains the property at XL 10, and the Ninja and Geek roles gain it at XL 15. Several other artifacts also confer warning as well:

The Flute of Slime (Acid Mage quest artifact, when carried)
The Cudgel of Cuthbert (Chevalier quest artifact, when carried)
The Harp of Lightning (Electric Mage quest artifact, when carried)
The Fire Chief Helmet (Firefighter quest artifact, when worn)
The Lockpick of Arsene Lupin (Locksmith quest artifact, when carried)
The Harp of Harmony (Musician quest artifact, when carried)
Blackshroud (Undertaker first sacrifice gift, when worn)
The Golden Whistle of Nora (Zookeeper quest artifact, when carried)
References

↑ include/display.h in NetHack 3.6.7, line 49

↑ include/hack.h in NetHack 3.6.7, line 494

↑ src/hacklib.c in NetHack 3.6.7, line 614: function dist2

↑ mon.c in NetHack_3.3.0, line 267

</color></color></color></feeling></feeling>