Ultima Online Detecting Hidden - the 4 tile passive radius, the 6 second timer, and the contest against Hiding

The passive half is four tiles wide

uo.com states it once and repeats it verbatim on the Stealth page: “The passive Detect Hidden range against a character using Stealth is a 4 tile radius.” The corollary from the other side of the fight: a stealther should stay at least 4 tiles away from everyone else.

That single number is the geometry of every stealth encounter in the game. Outside four tiles no passive check happens at all and your skill value is irrelevant; inside four tiles it happens whether you are looking at the right part of the screen or not.

[!] No tick rate or check frequency is published for passive detection at any skill value. uo.com says the radius; it does not say how often the roll inside that radius is made.

The active half is a reticule and a six second timer

Used actively, the skill gives you a targeting cursor and asks ‘Where will you search?’ A success reveals hidden characters and traps within the search range, with effectiveness decreasing based on distance from the point you targeted.

The hard limit is the reuse delay — “There is a 6 second delay between uses of Detecting Hidden” — which bounds how fast one person can sweep an area, and is why a group flushing a hider spreads out rather than stacking.

How far an active search reaches is unpublished: the radius grows with skill, reaching almost the full screen at Grandmaster [!].

[!] There is no per-skill tile table for the active radius — that description is the whole of it — and [!] the distance falloff is not published either. Any radius-by-skill table is unpublished.

What the skill is actually rolled against

Two different contests, depending on whether your target is moving.

• Against a stealther. uo.com’s Stealth page: “A check is made by comparing the stealthers Stealth and hiding skills versus the other persons or monsters Detect Hidden skill.” Both of their skills are weighed, against one of yours.
• Against someone standing still. The active version depends on how your Detect Hidden skill compares with the target’s Hiding skill — Hiding alone.

Two things follow. A moving target is contested by two skills added together and a stationary one by a single skill, so the character sitting in a corner is the easier catch. And because Stealth has a Power Scroll while Hiding does not, a maximised stealther brings at most 120 + 100 against your 100 — which is why Detecting Hidden is carried at a full Grandmaster or not at all.

uo.com also notes that a character under the Magery Invisibility spell is easier to detect than one using the Hiding skill.

[!] No success-chance formula is published for either mode. uo.com says only which skills are compared. There is no published percentage, no published skill-gap table, and nothing stating how far ahead you need to be.

Inside your own house there is no contest at all

This is the single most decisive published fact about the skill, and it is not a scaling bonus — it is an override.

Used in a house you own or are friended to, Detecting Hidden always succeeds — 100% [!], regardless of skill level. uo.com says house owners instantly reveal anyone hidden within their property; the useful part is that the guarantee extends to friends of the house, not just the owner.

One more detail changes how the skill behaves indoors: used inside a house you own, it searches for people rather than traps.

The consequence is blunt. A stealther cannot sit inside a house whose owner or friend uses the skill, at any skill ratio, ever.

The thresholds

Skill	What changes
20	Every human already has this much, free, through Jack of All Trades
50	Historically the floor for training Remove Trap, with 50 Lockpicking — see the note below
75	Passive detection of dungeon floor traps, other than in the oldest dungeons where traps are no longer hidden
80.0	Passive detection of Virtue vs Vice sigils, and of VvV traps
100	Active search radius reaches almost the full screen, unpublished [!]; also the cap, since there is no Power Scroll

uo.com on the 75: “Most traps in the oldest dungeons are no longer hidden, passive detection of other floor traps will only occur if a player has at least 75 detecting hidden skill.” The change dates to Publish 80 [!].

Traps, and the colours only one client shows you

uo.com states that spawning and static containers usually carry all three trap types, that tinkers can trap crafted lockable containers, and that a successful detection displays a [trapped] label. In the Classic Client only, colour names the trap:

Colour	Trap
Purple	Explosion
Blue	Dart variants
Green	Poison variants

Enhanced Client users do not get that cue. It is a published client difference, and for a treasure hunter a real argument about which client to run.

The damage figures are unpublished. Trapped containers deal up to 150 damage points [!], dungeon floor traps up to 60 [!]. The random floor trap spawns are the floor saw trap, floor spike trap, poison gas trap and exploding mushroom trap; once detected they become visible to everyone and disappear after several minutes. uo.com publishes none of it.

Detecting a faction trap reveals it to all nearby faction members for one full minute [!].

The hidden boxes

uo.com names two places where containers are hidden rather than merely locked: Exodus Dungeon and the BMV Ararat wreck. Each of those containers carries 2 traps — poison and explosion.

That is why the skill sits on templates with no interest in revealing players. Without it you cannot find the boxes; with it you still need Lockpicking to open them, Stealing to work the Exodus Zealots, and something to survive two traps. The Exodus boxes are also the published source of the parasitic plants that Poisoning turns into Parasitic Poison.

Humans start with a fifth of it

uo.com: “All human characters have Jack of all Trades of 20 Detect Hidden”. Any human standing near a hider therefore has a passive chance, however small, of ruining the approach — a stealther cannot treat an untrained human as a blind spot. Elves get something else: “All elven characters have a racial bonus increased chance to passively Detect Hidden”. [!] That bonus is given no numeric value by uo.com. It is described and not measured.

Two points that are not settled

Which ruleset turns passive detection off. uo.com states that passive Detect Hidden does not function in “Abyss” rulesets (uo.com Detect Hidden). [!] Unpublished: the same restriction also applies to Siege Perilous rulesets. Whether these are the same restriction under two names is not stated by uo.com.

The Remove Trap prerequisite. An unpublished rule has Remove Trap untrainable until you have at least 50 [!] in both Lockpicking and Detecting Hidden. uo.com’s Remove Trap page states “Until publish 105 there were ‘qualifying’ requirements which must be met before the skill could be trained, these have been removed” (uo.com Remove Trap). The 50/50 requirement appears to describe the pre-Publish-105 state, and uo.com’s is the more recent statement.

In PvP

• It is the only skill counter to stealth. Everything else that finds a hidden player is a spell, an area effect or a potion. This converts a stealther’s approach from safe to contested the moment they cross into 4 tiles.
• Four tiles is the whole negotiation. The stealther’s job is to stay outside it; yours is to make them come inside it, which doorways, chokepoints, boats and bank steps all do for you. The 6 second active timer then sets your sweep rate — one character cannot search continuously, so a defending group covers ground with more than one carrier rather than one person spamming it.
• Your house is an absolute veto — “always 100% successful”, at any skill ratio.
• Virtue vs Vice makes it compulsory. A passive check warns you near a sigil at 80.0, VvV traps are passively detected at the same 80.0, and the steal itself needs detecting hidden plus 100.0 Stealing. That is the published price of playing sigils.
• It does not cost you your own cover. uo.com’s Hiding page lists Detect Hidden among the skills usable while hidden without being revealed, so a hidden scout can sweep for the enemy’s hidden scout and stay hidden doing it.

In PvM

• It opens the Exodus loop. The hidden containers there and in the BMV Ararat wreck cannot be found without it.
• 75 skill stops you walking into floor traps, outside the oldest dungeons where they are no longer hidden. They deal up to 60 [!] damage.
• It tells a treasure hunter what they are about to disarm. The [trapped] label plus the Classic Client colour turns a Remove Trap attempt into a decision, and container traps deal up to 150 [!] damage.
• Monsters carry Detect Hidden too. uo.com’s Stealth page says the check is against “the other persons or monsters Detect Hidden skill”, so the four-tile geometry is a PvM rule as well.
• Scanning a room is free. Using the skill does not reveal you, so a hidden thief can clear a room without ever breaking cover.

Caps, stats and training

Primary stat Int, secondary Dex. Detecting Hidden has no Power Scroll — it is absent from uo.com’s published list — so it caps at 100, against the 720 total skill cap. There is no 120 of it to plan for. Scrolls of Transcendence do apply, since uo.com states they cover “all skills (including non-Powerscroll skills such as begging and remove trap)”. It has no Skill Mastery.

Training is done on trapped boxes:

Range	Method
0–30 [!]	Starting from 0 is very slow going; buy the first 30 from an NPC
to about 60 [!]	Boxes trapped by a Tinkering character of around 35 skill [!]
60 onward [!]	Switch to boxes made by a Grandmaster tinker
from about 50 [!]	Let a Satyr in the Twisted Weald use Discordance on you for faster gains

uo.com names the Crystal Ball of Knowledge as the aid, working on distance-based difficulty messaging “similar to a ‘hotter/colder’ game”, and names the hidden room at the Britain Warrior’s Guild as an excellent spot for this skill together with Lockpicking and Remove Trap. Factions are an alternative. Underneath it all the Guaranteed Gain System awards a mandatory 0.1 when nothing has been gained inside your bracket’s window, and a Scroll of Alacrity raises each check to 0.2–0.5 for 15 minutes.

What is not published

None of this is published by uo.com:

• [!] The active search radius in tiles at any skill value.
• [!] The success-chance formula for passive or active detection — only which skills are compared.
• [!] The numeric size of the elven passive bonus.
• [!] Any per-skill passive detection frequency or tick rate.
• [!] How an active search’s distance falloff is calculated.
• [!] Whether uo.com’s “Abyss” exclusion and the unpublished Siege Perilous exclusion are the same restriction.

Where these come from

uo.com Detect Hidden · uo.com Stealth · uo.com Hiding · uo.com Remove Trap · uo.com Skills, Stats & Attributes · uo.com Scrolls of Power · uo.com Scrolls of Transcendence · uo.com Skill Masteries · uo.com Skill Gain Systems. Everything here is from uo.com or the game itself; anything uo.com does not publish is marked [!] as unpublished where it appears.