I seem to remember having a book that spoke of magically active bacteria so that the spaces could not be viewed astrally because the bacteria blocked it. The people breathing the bacteria would not be affected so you could keep all of the office spaces filled at all times.

If I am not just making that up, couldn't you have a lower concentration and by watching the movements in the air you can tell when someone is there by the perturbations caused by movement and possibly breathing? Would not matter if you have silence spells, improved invisibility, levitate, and your own O2 breather, your presence would cause air currents that could be detected.

This is either 1 or 2 of the FAB strains. I'm not entirely clear on which does what except for FAB-III, which drains mana and impedes spellcasting.

One of the strains does exactly what you're describing - it flouresces as an astral body or magic passes through it.

Which book is that in?

Corporate Security Handbook
Don´t know if it was reprinted enywere else.

They did allso pump this stuff into Tanglerwebs to entangle Astral forms from the physical plane. Don´t know however if they kiked that compleatly with SR3

Okay thanks. I will have to look for that one. I was just thinking of ways to protect a facility from mages. My group tends to think more in CIA terms anyway instead of actually assaulting the building. This is more just to have something in place in case they do something to surprise me.

There are some other possibilities described in Magic in the Shadows, too.

Both books are rather outdated if You´r using SR4 though.

FAB bacteria glows visibly when an astral presence flies through it, allowing mundanes to detect astral intruders.

There are also types of dual-natured vines (and slugs too i think) you can use to block astral passage, which some corps may find cheaper than warding everything.

Also, it'd be very impractical to monitor "air currents" or whatever in any sort of room where people usually walk. It works well for safes and vaults, though.

The thought was to monitor it after hours when no one will be walking through.

Still easier to get a defector instead of hitting a hard target.

There is something called "glow moss" in YOTC for exactly this use. Its a moss that can be cultivated inside the walls (as to get licht for some houres to live) when something astral goes throu, it will glow, which can be detected by sensors and rais an alert.

Also, nothing says you can't invent some stuff either. My ghoul spy, which I sadly never got to play, decked his house out in astrally-active plants (he had the parabotany skill as a hobby) so his house was 'well lit' in an astral sense, and he could watch mana flow along vines and into blossoms and the like.

Of course, he lived in Australia, where wierd shit is de rigeur.