[Orvich]

Though as  a GM I'd rule that anything that doesn't break LOS in the physical plane (like a pane of glass) would break it in astral, provided the target is other-wise targetable (has an astral form).

[WellsIDidIt]

Anything can be used for cover on the astral plane. Living things give off their aura which blocks LoS. Non-living things are opaque and give off shadow. Glass, water, plastics, etc. that are transparent physically most assuredly block astral LoS. That's why ghouls stick to the underground in seattle...it's always raining shadows. 

[Orvich]

Well no. Shadows of things that are transparent normally specifically only impair astral vision, not block it.

From Street Magic pg 114:

Items that are transparent or mirrored in the real world  (like a car window) simply impair visibility as astral shadows.

In other words, not all shadows are opaque. Some of them are as the name suggests, merely shadows. Looking through a window on the astral plane would show the outside world, just through a thin grey film, like a claritin commercial.

The table on the same page indicates that there is a -1 to -4 penalty for 'shadow clutter', which presumably applies here. I'm saying that if I were a GM, I'd rule that a single window pane was only a -1 visibility penalty! Or less, situationally, as the shadow clutter visibility impairment is apparently intended for use when your target is moving about in a field full of parked busses (or something like that).

[The_Gun_Nut]

Fun fact:  Mirrors work just fine for targetting spells.  Both in the physical and the astral.

Go nuts.

[Mäx]

Fun fact:  Mirrors work just fine for targetting spells.  Both in the physical and the astral.

Go nuts.

But always remember that a fireball doesn't bounce of a mirror, it explodes right there.

[foolofsound]

But always remember that a fireball doesn't bounce of a mirror, it explodes right there.

But Lasers do!

[The_Gun_Nut]

Spells don't "bounce" off mirrors.  They follow the direct path to the target, ignoring intervening obstacles, except in the case of indirect spells.  Indirect damage spells conjure up an effect (ball of fire) and travel across the intervening distance in the physical world.  So in the case of casting a spell at a target on the other side of a wall using a mirror, think of it like this:

[Orvich]

No one said they did! There was only talk of targeting via mirrors, and the quip that fireballs don't bounce of mirrors (Which is entirely true!).

[The_Gun_Nut]

It was implied in the text.  Just clarifying.

[Black]

And remember, watchers are stupid as all getout.

That's putting it mildly.

Which is why my guys use their actual bound spirits for astral scouting.  Watchers are at best look outs for mundanes (tell me when someone who looks like x arrives) or annoyances and distractions.

[The Wyrm Ouroboros]

Well, my question is whether you're asking as a runner, or as a security guard, i.e. player or GM.  Answering #2 from a GM perspective, I give you the following:

A Zero-Zone with a monowire network.

Astral shadows are well and good, and a high sneakery rating is great too - but when you get down to it, the invisible masked adept whatever has still got to put his foot down somewhere in the 30m stretch of ground between fence-lines.  Drop a mathematically-erratic webwork of monowire in there, keep it only 1-2cm off the ground, and watch your stealthy ninja slice his foot apart.  Physically link the monowire ends to an alarm system, so if he's wearing boots that are for some reason impervious to wonderful Monowire Slicing Action, then the slight pushing down will trigger the alerts.

Alternately, 'seed' it with 'technorazor grass'.  10cm grass-sized monowire-edged and -tipped blade that juts out of its holder.  When not receiving the 'arm/disarm' signal, at least half of them default to jutting out; alternately, have them only accept a short-range (2m) signal normally found on their lawn mowers and security guards.  Place in a 1.5 to 2cm hex pattern, set at the same height the grass is kept.  They see security strolling across the ground, they decide it's safe ...

Remember, don't defeat the magic; defeat what the magic can't cover all at once.

[JustADude]

Well, my question is whether you're asking as a runner, or as a security guard, i.e. player or GM.  Answering #2 from a GM perspective, I give you the following:

A Zero-Zone with a monowire network.

Astral shadows are well and good, and a high sneakery rating is great too - but when you get down to it, the invisible masked adept whatever has still got to put his foot down somewhere in the 30m stretch of ground between fence-lines.  Drop a mathematically-erratic webwork of monowire in there, keep it only 1-2cm off the ground, and watch your stealthy ninja slice his foot apart.  Physically link the monowire ends to an alarm system, so if he's wearing boots that are for some reason impervious to wonderful Monowire Slicing Action, then the slight pushing down will trigger the alerts.

Alternately, 'seed' it with 'technorazor grass'.  10cm grass-sized monowire-edged and -tipped blade that juts out of its holder.  When not receiving the 'arm/disarm' signal, at least half of them default to jutting out; alternately, have them only accept a short-range (2m) signal normally found on their lawn mowers and security guards.  Place in a 1.5 to 2cm hex pattern, set at the same height the grass is kept.  They see security strolling across the ground, they decide it's safe ...

Remember, don't defeat the magic; defeat what the magic can't cover all at once.

You're forgetting one other thing: Auto-turrets (yes, plural) armed with grenade launchers set to spray the area where an alarm goes off.

I'd suggest loading them with Freeze-Foam... not to be "merciful", but because it's the least likely to compromise your defenses to further attacks before you can clear out the grid.

[The Wyrm Ouroboros]

Just remember that you can't mask as 'nothing' - generally you have to mask as something substantial.  Which means you're still spot-able.

[nmap]

Smoke grenades are pretty close to "technological defeat of magic" and they are only few nuyens each. Make it thermal smoke if you're facing a cybermage, wear a chamelen suit, ultrasound sensor and a monowire sword, and walk softly. He cannot kill what he cannot see and power has (probably) blinded him long ago. Grenade launchers work well too, mages tend to be weaker on dodge (no reaction 6+ like a proper streetsam), grenades have that annoying -2 to dodge for being area effect, so they get to know how it feels being hit by a fireball.

[WhackedMaki]

Smoke grenades are pretty close to "technological defeat of magic" and they are only few nuyens each. Make it thermal smoke if you're facing a cybermage, wear a chamelen suit, ultrasound sensor and a monowire sword, and walk softly. He cannot kill what he cannot see and power has (probably) blinded him long ago. Grenade launchers work well too, mages tend to be weaker on dodge (no reaction 6+ like a proper streetsam), grenades have that annoying -2 to dodge for being area effect, so they get to know how it feels being hit by a fireball.

Then they turn on their astral sight... and Manabolt you anyway. As long as they're still in their bodies, they can still hit you.