The ability to effortlessly locate all enemy units in the battle is as unrealistic as the flawless co-ordination of IGOUGO but we often disregard it in the interests of "playability." Sometimes it isn't about "stealth" or "invisibility" so much as acquiring a lock/firing solution - i.e. 2300AD assumes warships are "blips" as it's hard to truly hide in space - but it's another thing to lock a ship loaded with stealth and EW countermeasures.
There are plenty of methods to simulate the "fog of war." Here's two common ones:
WoW/2300AD use a similar method; there is a "fixed range" at which units are spotted, depending on type. I.e. in WoWS battleship is seen at 15km, a cruiser at 11km, and a destroyer at 7km. This range can be extended by factors like firing weapons (+4km) or in the case of sci fi, using shields, pinging with active radar, or passive sensor capabilities. Lightning Strike increases the "to hit" chance for every "noisy" action.
TFL games like BtH use blinds (cards or tokens representing the unit) which are moved around on the board and are only replaced with the actual model when enemies pass a spotting roll. Infinity uses a similar method for its stealth units. In many games there is no blind and being "unspotted" merely gives immunity from being fired on, but that rather spoils the surprise....
It's also usual in many cases for there to be a "auto spot" range at which units are... well, automatically spotted, and then a longer range where a dice roll is required. Some games go the "whole hog" use plotted movement but they tend to require an umpire/trustworthy opponents, AND a lot more time and complication than I care for.
I feel activation/initiative sequences can also mesh with the concept of detection, apart from the obvious things like bonuses/better control of activation sequence for unspotted units but let's stay on topic, shall we? (Because every game design topic tends to devolve into a discussion of everyone's favourite activation method in the comments, anyway)
The problem with spotting and detection...
(a) People don't tend to "expect it." Yes, it's weird, but how many rules (since the 80s anyway) have spotting rules by default? I know I raise my eyebrows when I "spot" detection rules in a rulebook I am reviewing.
(b) It runs headfirst into the "gameplay depth vs complexity" conundrum. Or to use my words, "decision points vs resolution time". Spotting rules add another thing to do. More measuring, more dice rolls, more modifiers - often *gasp* charts. Like stats, charts and modifiers, it is a "victim" of the backlash against the overly fussy rules of the 80s and early 90s. In the quest for modern streamlined rules, detection rules are often seen as an unnecessary step. Let's just skip straight to the pew-pew, shall we?
Since (a) people don't naturally expect it, putting spotting rules into a game is a bit risky, as they may perceive it as (b) adding unwanted "complexity."
So there's the challenge for a game designer: If you think your genre needs detection rules, detection has to add enough extra tactics and decision points as to make it "worth it" to people who may not see the need for it.
How do we make detection important?Here's a few example situations that would emphasize detection:
If weapons have a high lethality or can shoot as far as detection ranges. So not getting spotted is important - if you have a 50% lethality (chance to die) when you are spotted - your players will care a lot about remaining stealthy. If all weapons can shoot as far as you can see, having superior view range is, in effect, increasing your firepower/"gun range"/move:shoot ratio (perhaps allowing you a "first strike" or to "kite" your opponent; firing from beyond his visual range.)
But my game doesn't need those things?In your Napoleonic game, muskets might only be effective to 50m - far closer than the range you can see a bunch of guys in bright red shirts. So really, we can avoid detection rules for Napoleonics as the view range:shoot range renders it moot, right?
Well, that presumes no one was ever surprised or ambushed the Napoleonic wars.... ....and also presumes a lot about the terrain. The troops in the French-Indian Wars would certainly beg to differ on the importance of detection and concealment.
I'm not saying detection rules are mandatory. For example, if you do think detection had relatively minor or rare impact on your genre you could incorporate detection/ambushing into scenario design and game setup or as a special rule rather than make it an ongoing rule throughout the game.
There is a lot more to explore in this topic, but family life intrudes in the form of a bored 2-year-old....
TL:DR*Detection is a vital aspect of most eras and types of warfare, but most wargames ignore it
*Detection can link with activation mechanics
*Detection does slow down gameplay; especially as most players are trained not to "expect" detection rules, designers need to ensure the extra depth makes the tradeoff worthwhile
*There are a few ways to emphasize the importance of detection; e.g. lethality/weapon range among others
*Not all games require a dedicated detection mechanic; if it has rare/minor impact a dedicated detection mechanic might not be needed and can be replaced by other things
I guess the aim of this post is to bring awareness about an oft-overlooked area.