Bridging Wires

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Lynx
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Bridging Wires

Post by Lynx » Wed Jun 29, 2016 12:58 am

Alright, there's a topic for alarm aficionados to answer.
I'll give you this example. Make note that I have legitimate access to the inside of the compound at certain times, and at certain times not.
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We have this sticky situation. A fine quality window sensor connected to a wire that runs through the building and connects itself to other sensors.
Would it be possibly to simply do this?
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The system I'm looking at is actually mounted directly on the glass, so I'm assuming it's a proper shock-based glassbreak sensor, and at the very least, a hybrid acoustic/vibration sensor that will sense any attempts to break the frame of the window itself. I doubt that something that close to the glass is an acoustic sensor.
I've got not clue about the brand of the sensor, so - is it common for modern sensors to detect changes in voltage? Say V = IR, where I is current and R is resistance, and I bridge the connection with a wire of a slightly different resistance. This can happen due to it being of a different thickness than the original wire, is the sensor likely to sound the alarm?
Oh, and cutting the sensor itself - perhaps when cut from the power supply, and assuming the best of it, the sensor will have an internal power supply of it's own (backup battery) that will either send out an alarm to the central control unit or sound an audio alarm. How would I go about avoiding this?

The only ideas popping into my head at the moment are:
1. Covering the sensor in foil, hoping any signal it sends out doesn't get out. Not likely as it would get detected from inside rather quick.
2. Muffling the sound of the backup alarm with foam or something akin.

Oh, and if the system is really damn advanced, each window sensor sends out pings to the central control unit at regular intervals for checks. When, for example, unit #X fails to do so, an alarm is sounded and the responsible security firm investigates - no police - as an alarm failure does not necessarily mean break-in attempt.
Anyone here with more knowledge on bridging wires?
Don't take it too seriously, you're not coming out of it alive.

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Psychlonic
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Re: Bridging Wires

Post by Psychlonic » Wed Jun 29, 2016 1:39 am

Well your general idea for jumpering is generally correct, although the wiring can vary from system to system. Often the system runs off two wires in a sheath, sometimes I even see Cat-5 cable used (phone line) where only two of the wires are in use, but if you jumper both it effectively shunts that sensor. Theoretically. As you've noted, sometimes the system reads resistance changes. The protective element of this is called the 'end of line resistor' BUT the vast majority of buildings unless it has something important to protect wire this in near the control panel because it can cause many issues leading to false alarms. Chances are high your sensor is safe to jumper without worrying about resistance. Unfortunately, the only way you can be 100% sure your wiring won't cause a problem is to run a resistance check with a multimeter between the two points you plan to connect your wiring to and create your own counterfeit with the same spec.

Wireless creates a whole new problem but also new vulnerabilities as well. If you can find the brand in use, you can find out for sure but many glass break sensors run in the 320mhz range which is "eligible" to be shielded with aluminum foil IF you can sufficiently cover the sensor and if it doesn't get noticed in the meantime. The sensor can also theoretically be jammed as well by creating a high power jammer in the 320mhz range or even have it sweep to cover a wider EM range, but as far as I know this has never been done before and I don't know if it would set the panel off anyway or not. Someone else might have more on the matter.

On the bright side, wireless will surely become more dominant in the future for ease of installation. Finding ways to counterfeit the signals and jam as appropriate would actually make life easier for the operative. With wired systems, you have to be physically present to attack the system. Wirelessly, you don't.
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Lynx
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Re: Bridging Wires

Post by Lynx » Tue Jul 12, 2016 11:32 am

I've been looking at the brand, but they're too secretive to post any information about their products in public, leading me to believe that they offer their own or generic alarms.
Working quick I may be able to strip some wire bare and take measurements - this would have to be done within the course of 1 minute at maximum.
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Re: Bridging Wires

Post by noone » Tue Jul 12, 2016 8:32 pm

An interesting thing to do (if you absolutely can't disarm the system) would be to make the wires look like they've been chewed through, leading the owners to believe that their alarm system has been disabled by a rodent, and then coming for a visit the next night. This solution isn't preferable since it draws significantly more attention, would probably involve heavy scrutiny the night of the incident(and possibly in the near timeframe) and could end up with people watching the property until the alarm is fixed (not to mention that you have to find a place where the wires could've been reasonably chewed through by a squirrel). But, if you are out of options, this could be very well a good solution.

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