Monitoring Solutions

**broken link removed**

So I have an area behind my garage which is open to the alley in which I want to monitor. I am in need of something that has a very low probability of false alarms however have a very high probability of notifying me of a person in the monitored area, I know nothing is 100%. I have used motion detection in the past, however it's too prone to false alarms due to basic traffic in the alley...so I want to come up with a new solution.

Here is the info:
- area is 30' wide by about 20' deep (from the garage to the alley)
- small birds flying around in the area
- no stray trees or bushes
- environment -50 degrees C to +50 degrees C
- area ground is dirt
- area is cleared of snow in winter
- sometimes cars will be parked in this area, however I would still like the area to be monitored

I know the best alarm system is a layered alarm system, so I have been brainstorming a few ideas and thought of using:

Laser Fence (red lines) - 3 IR lasers (where can I find low cost IR laser diode?) placed 1' apart horizontally the length of the opening. Placed 3' back from the alley.

Ultrasonic Detector (green boxes) - pointing down from the garage onto the monitored area behind the lasers.

The reasoning behind the laser fence is to require each laser beam to be cut in order (#1 being the laser closest to the alley and all the way through). This would reduce false alarms due to birds, if they did manage to pass through one of the beams. Also the sensors for the lasers would adapt to the weather (due to snow or rain) since it will only count a cut beam, not degradation in signal.

The ultrasonics could be used in case if a car was parked behind the garage, cutting some or all of the laser beams, and the ultrasonic sensor could monitor the existing environment and if there is a rate of change beyond a specified value then the alarm would trip. Also if there was nothing blocking the lasers the ultrasonics could still be on to monitor the area between the lasers and the garage. In case someone slipped by or knew about the lasers (which 99% chance they won't).

All these inputs and outputs (for modulating the lasers) will be controlled via a microcontroller and the output will be sent wirelessly to the house with an "alarm box" that just highlights which zones have been tripped.

What do you guys think?

Any security system that complex is going to be neither reliable nor resistance to false detection.

Sceadwian said:

Any security system that complex is going to be neither reliable nor resistance to false detection.

Click to expand...

What do you suggest?

I figure it's simple in terms of 3 light beams and 2 ultrasonic detectors. I am not very familiar with ultrasonics as of yet, however I could strictly go with the 3 beams and write code so the beams must be cut in sequential order to trip the alarm. Seems fairly simple and foolproof since the chance of false alarm would be quite small due to the coding. The sensors and lasers will be installed in sch 40. pipe which will be welded to a bracket which would allow it to be mounted to the fence (which is very solid).

WHy do you even need 3 beams? Just use one beam placed at 3 feet. How many people are going to enter a garage by stepping higher or crawling under a beam that they can't see placed at a height of 3 feet? I don't know any cats or dogs that are taller than 3 feet, nor any reasonable birds that are taller than 3 feet, hop higher than 3 feet, or attempt to take flight inside a garage. Then, you coud also use a pyroelectric sensor that would only turn on the beam when something was detected to reduce false alarms from snow and hide the beam even more. Or, you could have both on all the time and both have to trigger for an alarm to sound.

Don't use ultrasound. ACtually before I say that, I don't understand what you mean by rate of change. A ranging sonar is not reliable enough or accurate enough in those conditions to do something like that. And if a car blocked the lasers, why wouldn't it block the ultrasound? Also, no ready-to-use ultrasound that I can reasonably get my hands on is operational across that temperature range, nor outside...during the rain. THere are a few, but they have some fancy driver circuitry behind them (they are electrostatic, see) which isn't overly readily available. If you're curious, go to SensComp.

Here's an example of an ultrasonic movement detector:

https://www.electro-tech-online.com/custompdfs/2007/08/k49.pdf

It does work (I've built it), but it's very power hungry. I can't say if it's suitable for long-term use, but it will detect movement at a range of about 10 ft.

Re-evaluate your goals and find an alternative sollution?
What exactly is the reason for monitoring traffic in this area?

dknguyen said:

WHy do you even need 3 beams? Just use one beam placed at 3 feet. How many people are going to enter a garage by stepping higher or crawling under a beam that they can't see placed at a height of 3 feet? I don't know any cats or dogs that are taller than 3 feet, nor any reasonable birds that are taller than 3 feet, hop higher than 3 feet, or attempt to take flight inside a garage. Then, you coud also use a pyroelectric sensor that would only turn on the beam when something was detected to reduce false alarms from snow and hide the beam even more. Or, you could have both on all the time and both have to trigger for an alarm to sound.

Don't use ultrasound. ACtually before I say that, I don't understand what you mean by rate of change. A ranging sonar is not reliable enough or accurate enough in those conditions to do something like that. And if a car blocked the lasers, why wouldn't it block the ultrasound? Also, no ready-to-use ultrasound that I can reasonably get my hands on is operational across that temperature range, nor outside...during the rain. THere are a few, but they have some fancy driver circuitry behind them (they are electrostatic, see) which isn't overly readily available. If you're curious, go to SensComp.

Click to expand...

The reason for 3 beams is to reduce false alarms, having a bird fly through a single beam will set the alarm. However the chances of it flying through all 3 are slim, especially in the correct order. However an unsuspecting person would cut the beams in the correct order which would trip the alarm. The reason for 3 is to reduce false alarms.

As for rate of change...if a car pulled up it'd trip the alarm. Then once the alarm shut off (say after 30 seconds) then the alarm system would adapt to it's new environment, so it'd see if any of the light beams are cut, if so then it'd ignore that part of the alarm. If a car was behind the garage then after the alarm shut off the microcontroller would take the new input for the ultrasonic sensor as the baseline, if it changed from that (either the car leaving or a person walking by) it would trip the alarm again. That is what I mean by rate of change.

I will take a look at a pyroelectric sensor as possibly a replacement for an ultrasonic setup. What is the exact sensors used on automatic doors at the mall? Something like that seems quite reliable in the rain and extreme weather.

pc88, thanks for that link. I am not too concerned about power useage as it'll be tied into the garage wiring, so there is no issue about battery life.

Sceadwian, well what do you propose? Right now the posted idea is my solution and I want people to critique it as to what would work better in my scenario. As for the reason for monitoring this area, I have a lot of very valueable equipment and parts (mine and my customer's) in my shop and I need a very reliable method of knowing if someone has approached the garage from the rear.

Hello,

You can tell by my name that I am in the alarm business. Going on 33 years.

Why don't you just buy some outdoor rated electric eyes. They're made for this type of application. They hace circuitry in them to ignor birds flying through the beam. If you want to attempt to eliminate false alarms, then by two or three of the and criss cross the beams.

A B

B C

C A

Then you can parallel their outputs together so that all three must be in alarm before you actually have an alarm event.

Ultrasonic is based on sound waves being disrupted. Very bad choice for outdoor use as wind will set them off.

Use Google to search for DIY alarm device suppliers and ask for Outdoor Photoelectric beams.

This should handle your needs.

HTH

AlarmMan

Conrad, how about just makeing the building as difficult to break into as possible? There's an AV place right next door to my work that was broken into 3 times before they realized all the cameras and alarms in the world won't make up for 4 inch thick glass windows and steel doors with deadbolts.

Sceadwian said:

Conrad, how about just makeing the building as difficult to break into as possible? There's an AV place right next door to my work that was broken into 3 times before they realized all the cameras and alarms in the world won't make up for 4 inch thick glass windows and steel doors with deadbolts.

Click to expand...

It is difficult...the only way in is by driving a vehicle in through a wall or the garage door. The doors are impossible to kick in, windows have bars and expanded metal mesh covering them. The garage is also monitored by my alarm company as well. Trust me the shop is secure...but I want to catch someone in the act without being prone to false alarms.

AlarmMan, very good to know. Any particular units you'd recommend? The alarm system I have installed in my house/shop is one of the latest DSC units. What type of output would a DSC outdoor motion detector have? I am not familiar with alarm system security standards, such as output voltages or how signals are being sent to the control panel. Anything you can share?

Hi Conrad,

Optex makes various types of outdoor photoelectrics. They make small units ranging in price from $90 on up to a little over $300 for a 500 foot beam. They also have a heavy duty industrial beam called the RedNet but my supplier didn't put the price in the catolog. If you went to the Optex website I'm sure you'll find something.

Now if you want to catch someone in the act I then would recommend day/night cameras connect to a DVR with motion detection capability. (Actually most good DVR's have that capability already). Day/night cameras adjust themselves to changes in background light. You could also consider using an Infrared Light in addition to the cameras. They make the area of view look like day light to the camera. You get them on camera and you got em! A good 4 camera system with DVR will cost around $2000.00. SuperCircuits.com sells a wide variety of systems and covert cameras as well as the lighting systems I mentioned.

Alarm equipment runs on several voltages. Alarm control panels have a 16.5vac class 2 transformer that gives the system 12vdc to power devices up to the limits specified by the manufacturer. Most alarm panels are able to provide up to 650-750ma of current. It is always wise to do a standby and alarm battery calculation on each job to make sure the system will work properly when you need it to. In other words, don't overload your aux power circuit or else the battery won't get the proper charge it needs. Fire alarm panels generally run off of 110vac and produce 24vdc for the devices that need power. They still make 12vdc fire panels for small jobs. Battery calculations are mandatory for fire alarm systems. It's you neck on the line if the system fails to perform.

Most of the photoelectrics that I have worked with in the past had their own built-in power supply meaning it had an AC stepdown transformer and backup battery for both the transmitter side and the receiving side.

Hope all of this helps you out.

AlarmMan

Oopps, almost forgot, These devices have relay contacts meaning you get both normally open and normally closed contacts so they can accomidate virtually any type of system including DSC. Don't forget the end of line resistor (EOLR) at the end of the loop. Outdoor units usually have a disqualification output that tells you when the beam is between 95% and 98% blocked and the blockage occurred slowly like during a snow storm.

AlarmMan, excellent info! Wow the Optex is nearly what I was looking at in terms of building. The only difference is that my setup would not be solar powered (too easy to have a solar panel vandalized) and have a much closer range. So for it's "photo-electric" beam, what would be the emitter and detector of choice for a setup like that? The Rednet looks to be more of what I want to do, just need to figure out the proper emitter and detector sensors and then I can do the rest. It states that it is modulated IR, gues something like a photoelectric beam used on a garage door would be perfect in this case. Any place that sells emitter/detectors like this?

As for catching someone in the act, right now I want to build this "alarm box" that I can keep in the house or shop which will notify me which zone has been tripped outside. Then I do plan on purchasing an IR night vision IP camera system (hidden inside a fake birdhouse) mounted a 15' tall post which will give me full view of behind the shop and the whole backyard. That way the alarm box will notify me which zone has been tripped and then I can monitor it on a touch screen monitor tied to a PC on my home/shop network.