Electronics > RF, Microwave, Ham Radio

Detecting very low power motion sensors

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glradio:
I have a TinySA Ultra with firmware updated to version 1.4-156 with which I can detect the transmission frequency of all devices at my disposal (remote controls, wifi routers, alarm sensors etc.)

The company that has deployed the alarm in an house under construction in 2011, has hidden several radio motion sensors inside the walls, simply by sliding the devices inside the brick cavities that were then plastered !

Some sensors activate the alarm at a distance of 1.5 meters, others even as close as 60 cm, so as to detect the passage of people accurately and only at certain strategic points such as hallways, stairs and other transit points, even outside the house.

The problem I’m experiencing is that I cannot detect the transmissions frequency of these sensor. I’m using the TinySA Ultra stock antenna with these settings: frequency span 100 MHz, Hold+Max Hold, RBW 300 KHz, LNA=ON (LNA OFF above 6 GHz).

As I get closer to where the sensor is located, I would expect to see a stationary signal which must decrease in intensity as I move away, but I can't see nothing !

Since I don't know anything about the type of sensor and its transmission frequency, I focused my attention on frequencies typically used by these devices: 2.4 - 3 - 5.8 - 10.5 GHz, then also the entire spectrum supported by TinySA Ultra up to 20 GHz.

What is the best strategy to detect the signal ?

Which antenna should I use for the purpose ?

Psi:
Are you reviewing raw data dumps from the TinySA or trying to find it on the screen?

It's probably an extremely short pulse or burst every few seconds to save power.
So you'll never see it on the screen except maybe with some sort of peak hold mode.

EE-digger:
Assuming that for battery life, 2011, yikes, I think you may want a RTSA with spectrogram or waterfall display.

But in addition to this, you may want an H field sensor that's well shielded, in order to block most of the ambient, or else you will be swamped by all the things you mentioned ... that neighbors own.

Why would they be tucked in walls permanently?  Were they for the benefit of the builder, say, for security during construction?

Bud:
What is on the recieving side? You may get some clues checking the reciever construction, antenna and board.

Edit: assuming the sensors are wireless.

coppercone2:
maybe you should use a metal detector if its on brick it might show up because their metal specific now. might have a weird reading not similar to rest of wall. find at least 1.


i would be pissed if the construction company left batteries in the walls WTF. sounds like you can find 1, go to a lawyer and have them find the rest, instead of wasting your time

I think it would make anyone anxious that some foreman is getting information about your buildings occupancy after they are gone. I would also get it checked out for microphones  ???

its lithium primary cell, they have steel bodies because its really flammable (elemental lithium)



these devices chirp also, very similar to a bird. you need to narrow down on the frequency and scan it high to catch it. try catching your cell phone, it also seems to do this. you get bursts when you access info (i.e. view a page).


and are you sure this is real? it kind of sounds like a prank. construction companies are cheap as fuck

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