What makes a good motion detector?

[stealth]

My players are fighting ice-world aliens that don't show up on infra-red. I'm thinking hand-held radar, with lots of signal processing so it works indoors, maybe TL-11 to 13. They can't get anything higher tech than 13, so a hand-held densitometer is out of the picture.

Anyone got stats, or a canon price?

 

[aramis]

passive sonar, seismic sensors: both can readily detect motion, both can be spoofed, but it requires slow, steady, quiet movement.

Active sonar also can be used. Low frequency can function much like a densitometer, generating a 3D image even through walls.

 

[Rover]

Sonar won't work in a vacuum. I was thinking laser motion detector or a thin wire attached to a claymor mine.

 

[aramis]

Sonar won't work in a vacuum. I was thinking laser motion detector or a thin wire attached to a claymor mine.

Seismic works just fine, so does passive sonar if the mics are in contact with the floor

 

[stealth]

Well, that leaves out seismic.

Seismic works just fine, so does passive sonar if the mics are in contact with the floor

I guess active sonar and backscattering lidar are the way to go for Aliens style motion detectors. Cr 5,000 doesn't sound like too much to pay at TL-12 for a 1kg hand unit. I suspect the one from Aliens was active sonar....

Also, the lidar unit would be blocked by doors and walls. So I guess active sonar.

 

[aramis]

I guess active sonar and backscattering lidar are the way to go for Aliens style motion detectors. Cr 5,000 doesn't sound like too much to pay at TL-12 for a 1kg hand unit. I suspect the one from Aliens was active sonar....

Also, the lidar unit would be blocked by doors and walls. So I guess active sonar.

For aliens, yes. For a vacuum capable, no....

Seismic and Passive sonar, You'll wind up with wheels functioning as microphones, and a handle/display unit, and get a similar reading, but only when not moving. Think a luggage cart with a display.

 

[Spinward Scout]

I suspect the one from Aliens was active sonar...

The one in Alien was described in the movie:

detects micro-changes in air-density

 

[stealth]

I didn't buy that and neither did the the characters:

detects micro-changes in air-density

riiight...., they said.

But that was Alien, and the device the android came up with (and we already know its agenda) was very suspect.

The motion tracker in Aliens had to be different - it could sense moving objects through walls.

I'm going to go with a TL-13 active sonar building a realistic scale model in holospace of the threat, that functions as a directional seismograph if you put it on the ground. Ground penetrating low-frequency waves should have no problem bouncing off nearby structures, and combined with modern signal processing I don't see why a map can't be generated.

A map with aliens on it.

 

[Enoki]

A simple "interference" detector. sound, microwave, or some other emmitted signal is used omnidirectionally. Anything that gives a doppler return off the signal is detected and using a directional receiver the direction of the return is noted. Anything not doppler would be rejected as non-moving.

 

[Spinward Scout]

Anything going through walls would have to have a radiation component, I'd think.

 

[aramis]

Anything going through walls would have to have a radiation component, I'd think.

Actually, vibration decoding is far more able to determine both movement and structures thrugh intervening material than most EM-radiation stuff. It's just much more computationally intensive.

I've seen a demo able to track a guy moving 2 floors down.

 

[Dragoner]

A super small microwave cavity magnetron seems the ticket to me, TL 10 maybe?

 

[Enoki]

Anything going through walls would have to have a radiation component, I'd think.

Why? You can currently use a laser against say a glass window and with extant technology listen to people in the room on the other side. The amount of power output for a omni-directional device working off a generated signal that uses a doppler effect return could be fairly to very low in as much as it is the sensitivity of the receiver that matters.
Modern radios detect microwatts of power. You can generate very low amounts of very, very high frequency radio energy with solid state equipment. You wouldn't need a cavity magnetron or travelling wave tube to make that happen.
So, to the extent that there is only one interviening structure or wall you likely would have some ability to detect motion through it depending on the sensitivity of the equipment and the composition of the structure itself. The more solid and non-rf / acoustically asorpbent it is the better the return.

A variant of this in situations where you have background signal to begin with would be to use a receiver that could discriminate among them and then use those signals for your doppler return. Then you wouldn't even be transmitting. That would make your device passive and stealthy on top of giving you motion detection.

 

[samuelvss]

Geese!