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So.. There are household alarm systems (to defend against burglars) which send SMS/e-mail alerts if an intruder has been detected or an alert is trigged.

However, Mobile networks can be jammed, and the phone lines and ethernet cables can be cut. Also wireless networks like WiFi (which rely on the hard-lines anyway) could be jammed too leaving the alerting in a useless state.

Is it possible that an attacker with low budget tools can stop the system sending alarms?

How can this be avoided? Are there any communication solutions that cannot be jammed or DoS'd?

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2 Answers 2

up vote 5 down vote accepted

No, there is no way to communicate without being jammed.

You can create redundancy so that the system has several ways of communication. If the system detects that any one way is jammed it can send an alarm another way.

Another possibility is to send the alarm from an external system. Your alarm system regularily contacts the external system sending a status and the exteral system sends an alarm if either a message indicating an alarm is received or it receives no message for some time.

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Doing "heartbeat" like stuff is a very good point, so that there will be an alarm, if no heartbeat received. –  gasko peter Aug 27 '13 at 10:08
    
@gaskopeter the problems with heartbeats is that A) they aren't constant (sometimes every hour, sometimes every 24 hours) and additionally, they are possible to record and replay (thus nulling the security...) –  NULLZ Dec 26 '13 at 1:59

What you want is back to base monitoring where your alarm system will 'check in' with your alarm monitoring company every 'x' minutes/hours to confirm that everything is still functional and that 'nothing has changed'.

If your concerned about phone lines being cut and signals being jammed you should be similarly concerned as to how the attacker knew the location and specifications of all your systems. GSM, 3G and 4G (and depending on country, CDMA) signals will all need to be blocked as the frequency bands are actually quite wide and these days quite difficult to block unless your attacker is a electronics engineer (that being said, most jammers are fairly low powered unless you have $$ to spend).

It should be possible to harden phone lines (up to a point buy digging them deeper, putting sensors around them, limiting access etc) but at some point they'll always run into the street so there's not much you can do about it if the attacker is determined.

As Uwe says, redundancy is your best bet, layers of different defences will make the system resilient against attacks but nothing is perfect. That's why banks get attacked. If your house is using multiple forms of alarms and CCTV however, its unlikely that you'll be targeted for a 'general' break and enter as it's to much effort for an opportunistic thief

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