[Hobbes]

Patrolling Spirits, Watchers, and Mages would still see the spell on the Astral plane.  The spells would still leave a signature behind that could be tracked. 

And wards are on the low end of security costs.  Riggers, Hosts, and Deckers cost more.  Having 24/7 Mall Cops on site costs about as much as a ward does.

Also for just a single room, use a Lodge.  500*Force for a permanent Mana Barrier.  Couple for the Executive Offices, one in the Security room, and another in a conference room?   If the entire facility doesn't need to be protected, then don't.  The Wage Slaves in their cubicles are all in VR, who cares if someone is listening to them lay there. 

[Stainless Steel Devil Rat]

Agreed.  Wards, even impermanent ones that have to be refreshed once or twice per month, are cheaper than hiring enough mages for astral patrolling. Employees gotta get some time off, and when you've got a skill set as valuable and as rare as being a magician... well you can leverage some good PTO into your contract, not have to work crazy hours, etc. Which means you need lots of mages to ensure schedule coverage...

OTOH having a contractor swing by twice a month to refresh your ward(s)? Freakin' cheap in comparison.  No salary, no benefits, etc.

[MercilessMing]

I almost never pay attention to Detection spells, because well, assensing exists, but the more I go back and read the CRB spell list it seems like you could write an errata doc just on this section.
The overview should talk about subjects and targets.  Detect Enemies, Detect Life, Detect Magic, should all talk about whether the targets get resistance or not.
Detect Magic says it "alerts the caster" but probably should be "alerts the subject" and it seems weird that reagents are categorized as active magic.

[Xenon]

SR6 deliberately removed several clarifying rules that was found redundant. This was probably made in an effort to make the book easier to digest -  but it actually made the edition ambiguous and harder to understand (not easier).


For example SR6 left out the fact that all detection spells except Clairaudience and Clairvoyance are considered "active" and are thus "opposed" (and can be counter spelled).

And it also left out the fact that if a detect spell affect more than one target then you roll once and compare hits against each target individually.



Detect Enemies give the willing subject of the spell the sense to detect if there are living enemies (not traps) within range. This is resolved like this:
1. The original magician roll Spellcasting + Magic. Note number of hits.
2. For each potential target that is getting close to the subject roll Willpower + Body
3. Compare hits. If the spell is successful against a specific target then detect enemies spell will inform the subject that there are enemies in the vicinity as soon as at least one valid target is within [the original magicians Magic rating + Net hits against this specific target] meters.

Note that (perhaps depending on your reading) Detect Enemies does not pin point where this enemy is or how many enemies there are within range. Just a binary "yes, there are enemies within range" or "no, there are no enemies within range". Think of it as the dagger / short sword that Frodo had in Lord of the Rings that could detect if Orks or Goblins were close by and if so would lit up with a blue light.

Detect Magic says it "alerts the caster" but probably should be "alerts the subject"

Yes, it should read "subject".
(not sure why they changed the wording from Subject(SR5) to Caster(SR6).