Alarm System and Detectors

Hi Folks

I need help as a recent incident has alarmed me in to taking action. The incident being that some thieving b******s recently entered my premises and managed to steal the lead coverings over the bay windows – all this while the family were asleep inside!

So now, from having zero security, I have been forced into considering systems that will alert me to intruders/burglars so that I will be able go out and hack their hands off with the chopper I keep under my bed! My concern is that I don’t want to be wasting precious sleep and energy hacking at cats, foxes, leaves and plain old air, so I need to know of known detectors that are reliable and function well. Circumstances are such that I will need to use at least a couple of wireless detectors as well as wired, as the front, side and rear of premises need protecting and cable runs are not going to be easy.

Currently I am considering the Scantronic 9751 hybrid system as this allows zonal expansion using an RFX expander, as ideally I would like to make the external detectors chime on individual zones. I would like to know if the above mentioned is a known good reliable system and which detectors would best suit my purpose. Currently I am only aware of the Optex VX402 which may suit my situation – are there any other ones?...preferably cheaper!

sorry to hear of ypur plight, but ypur plan is flawed.

You can't use internal detectors outside
they are not designed for it, and if you did try would be unreliable (trust me i have seen it done)

wireless detecors are virtualy useless, and again they are internal detectors

You have 2 options left but neither are cheap.

the only reliable detector for outside use is an active infra red beam, but as leaves can set it off (wind and rain can't) you need 2 of them



you can get double beams but in my opinion they are too close, hence use two single beams.

The other thing you may wish to consider is cctv (maplins do a whole range of it)

Either way it will not be cheap, but it will be reliable


they are so good and reliable airports use them, although on a bigger scale

The other thing you may wish to consider (depending on your location) is physical security, such as gates, barriers, trellis and rose bushes

Many thanks Breezer.

Can you clarify regarding the PIR point. Are all external PIRs useless per se?...I ask as the VX-402/402R are marketed as external detectors and at a hefty price too! Doesn't this dual technology/zone stuff make them reliable? The same should be asked of wireless detectors regarding the cost.

The infra-red beam system is a possibility. I assume it would not be wireless and would need a separate transmitter(s) and receiver(s) setup. Also, if incorporated into the alarm zonal system a dual (two beam) configuration would have to rigged so that an alert is triggered when both beams are broken together - am I right? Can you please post links to available systems and where they can be bought.

I wouldnt say all external pirs are useless, just most of them.

By design any pir will be suseptable to wind / rain (setting them off)

In theory a duel technology detector is less suseptable to false alarms, since it relies on both technologys "seeing something" to cause an activation, but they can still see birds, foxes virmin etc, assuming you can find one that claims to be suitable for exteral use (i am not familiar with the one you mention) also it is a known fact that microwaves will creep over time, that is to say you adjust it to pick up say 10 feet max by next month it may be 10 1/2 feet.

also microwaves are refelected by anything metal (its how some speed cameras work)so if a tin can gets blown into your garden the microwave part will go off, and the pir will becuse of the wind.

It is also why as the picture i linked to shows the cheaper end of perimiter protection is always active infra red beams becuse they only suffer from snow frost, whch is overcome by an intermal heater, fog / mist no problem

There is lots of info on this forum about radio detectors, so i wont geo there again at this time

You are also right about the beam set up (to a point)

Idealy each pair should be on its own cct, then when set, the panel will not create an alarm condition untill both beams are simultaneously broken, but not all panels can do this

There are lots on the market if you google for them, i do not want to appear to be biased.

if they are for short distances you may also like to consider the ones used for automatic sliding gates, since they are the same thing, only smaller

Cheers Breezer

As with most things, nothing is straightforward...looks like false alarms are inevitable...will have to share alert response duties with the Mrs!

Anybody know if the Scantronic 9751 panel is good and if it accepts the dual (separate circuit) IR beam configuration mentioned by Breezer?...also I would like to know if anybody has any practical knowledge of the effectiveness (against false alarms) of the VX-402 external PIR.

I just read up about the pir, i smelt something funny about it.

It also doesn't mention about wind and rain imunity, i wonder why

I would say you're trying to over egg the pudding slightly here.

Super cheapy way:

300w floodlight with plug in chime unit. £30 tops all in? Should scare the buggers away and alert you at the same time which is what you want by the sounds of things.

If you still want something to integrate with your intruder alarm, get yourself a GJD Opal Elite PIR. Very reliable and will rarely false alarm if set up correctly (I have a couple on my house triggering lighting and CCTV with no false activations). You should set the PIR as chime or internal alarm only.

A set of Infra Red beam pairs is slightly OTT in this situation. They are quite expensive and they look awful too. You may struggle to line them up too unless they are very close to each other. The single beam types can be hopped over/crawled under pretty easily aswell....

beams are easy to set up, not as hard as you seem to be making out, i also said one beam was not a good idea, i also said they are not cheap, but very reliable

gjd kit is ok, but unless the "control key pad" is next to the bed they are a bit quiet.

i have also seen gjd kit "false alarm" alot, but yes it is another (cheaper option) but not that good

I was wondering if anyone had used the Risco Watchout detectors:

http://www.riscogroup.co.uk/Products.aspx?proid=69

Blurb says they're ok for pets, rain, tree sway etc.

not if you read all of the blurb it doesn't

they also dont mention that microwaves and pirs can see rain

buy one and try it and let us know what happens