Now that I've actually laid hold of some of the books, can you page ref that for me? It's a big change from SR2, where thermo saw straight through Invis or Imp Invis.

1. Pressure detects them fine, IR & thermo no, they're the same thing btw, and ultrasonics yes.

2. Perception. Sensors don't roll, I myself add 1 or 2 to the TN to spot the person in the first place, as sensors include a variety of non-visual detection.

3. Only if they're astrally perceiving.

Yeah, in my games there used to be an average of one of either per patrol in mid-level facilities (lower level ones couldn't afford speciality recruitment, higher level ones were as likely to use cybereyes).

No, they aren't although SR uses the terms interchangably ...

They are merely based on the same physical phenomenon: electromagnetic waves within a certain range of wavelengths (can't be bothered to search for the exact values right now).

The difference is however:

IR cameras and diodes *like in your IR remote control* (and presumably a natural occuring form of IR-vision, if such existed *not to confused with IR perception of snakes*) operate directly on electric currents produced by incoming IR waves. It's a normal, socalled photo effect. The heat transfering effect of IR is next irrelevant for that kind of application. All that matters is that the receptor material produces voltages and currents based on the wavelengths of the incoming light.
Camera systems that work with that kind of technology usually provide black and white pictures although it would be possible to make "false color imagery" just as with what I'll briefly explain in the part about thermographics.
This technology usually uses wavelengths that fall in the realm of socalled short or near IR ...

Thermographics (at least the conventional form) works more indirectly. It meassures temperature differences created by IR light within receptor materials and references them to a know heat source. This time it's the heat transfer effect that's being used to make the "perception".
This technology usually is connected to those colored pictures as used in Robocop or Predator and even went into the description if IR-Sight in M&M on p. 49 (although at least the biological version is more likely to operate on the previously mentioned photo effect that has nothing to do with temperatures).
This technology makes use of wavelengths in the mid to long range part of the IR spectrum (The longer waves transfer significantly less energy but simultaniously aren't absorbed as easily by the sourrounding atmosphere ).

How's that reflected in SR?

Pretty simple: The Thermosense Organ bioware operates on the thermal effects of IR and can detect persons under invis spells (although with less precission). Any technical sensor that operates on the same effect will still be able to thermally detect persons under Invis or Improved Invis.

"Optical" sensors that use the photo effect however (e.g. IR light barriers) will be affected by the improved spell version since they operate on what SR considers as "Sight" ...
Since natural and cybered "thermosight" in SR no longer are unaffected by the invis spells (in contrast to SR2, where thermosight defeated the Invis spells), I consider those forms of IR-perceptions as also being based on photo effects, despite the M&M description ...

Improved invis fools the mind of the viewer into not seeing the target of the spell. So yeah, pressure traps/detection would be activated. I'd argue that if something has been paid for with essence (cybereyes, natural vision, etc.) that it would be considered "vision" on the part of a character as be subject to the spell. If the detection method was non-living (external detection system) then it would be subject to the standard threshold for illusions vs. non-living viewers.

As a note, the latter part may not be how canon dictates thermo/ultra, but it's an easy ruling we use.

Living targets make an Intelligence (Force) Test and must beat successes genreated by the spell. Since non-living viewers don't get resistance tests and are either effected or not, so the spell must be cast at sufficient level that being, Object Resistance/2. Cameras have OR=8, so a Rating=4 spell or higher would be needed. The whole "OR or not OR" argument is questionable, otherwise, the spell would auto-suceed no matter what level.

Illuisions are obvious on astral and cannot diguise or create auras so, yes, Invisibility (or any other illusion) is useless against Astral viewers.

Regular Invis effects only living targets.

Improved Invis effects living and non-living targets.

My argument about regular invis affecting cybereyes was that since they've already been paid for with essence, they should be coinsidered "living" for purposes of Regular invisibility.