Perimeter IDS On Security Fence

In high security installations (e.g. nuclear facilities) generally it is possible to find no.3 levels of fence: the outermost, the median and the innermost.

In this case on the median it is installed the PIDS, while the outermost has the function to avoid that debris, small animals and other interferences can raise false and nuisance alarms, and the innermost is the delay element for the intruder, once detection is accomplished.

Also, between the median and the innermost are installed other sensors (e.g. microwave barriers), that have the function to confirm or not the intrusion attempt.

But what about when you have only no.2 levels of fence?

you can apply the PIDS on the outermost, and in this case you will have the innermost as the delay element, but with good probability you will have a raising in false and nuisance alarms, due to the missing function seen before ( to avoid that debris, small animals and other interferences)

- OR -

you can apply the PIDS on the innermost, with the outermost having the the function to avoid that debris, small animals and other interferences can raise false and nuisance alarms, but you will loose the delay function of the fence behind (from outside to inside) the one where the PIDS is applied.

where would you apply your PIDS having only no.2 levels of fence?

thank you for share your thoughts


If I only had two levels of fence, which is not uncommon here even in very high security installations, I'd always put the fence detection system on the outer fence. Otherwise, there is little point to having the "no man's land" in between the two. I've also seen two fences put up with no sensors on either fence, and only microwave or buried cable between the two, to detect when the intruder hits the ground. It's less time for response, but it's definitely less prone to nuisance alarms.

Also, you could very well end up with false alarms from birds or rodents on the inner fence, as many of them can slip under/through the outer fence. I know of at least one place where this was happening.

Working around nukes in the AF years ago we always had 3 levels of detection or threat levels .

Since this is NERC Reg. Area

1st line , 2nd line , 3rd line

perimeter , microwave & Ground protection

fenceline , fence itself

inner areas ground detection & laser site detection & Microwave .

Use a capicitance proximity detector , so that when you touch the fence you create an alarm condition .

Company in reno , nev makes these products .

We recommend Southwest Microwave and Protech.

Thank you all for sharing your thoughts! Focus here is on the methodology, I'm not looking for manufacturers. Thanks

WHat is on the outside of the outer fence? That should determine the feasibility of putting IDS on that fence. If it's lots of open area, where no one should be anyway, like a border situation, but also a waterside faciltity, then maybe the outer fence works. But if it's public and busy then you will get all those false positives. For example I once did an airport where outside that fence was a public parking lot- way too much activity and autos hitting the fence to make any sense. In that case you can cover your no mans land between the fences as the warning and then activity on the inner fence as your alarm. At the airport there was minimal normal acitivty on the inside. Also consider the normal activity inside the innner fence, since as noted above the animal action might be equal on both fences and cause the same false alarms. In a prison, there's a lot of activity on the inner fence and a lot of free space where no one should be on the outside.

thanks Marc, for your insight.