Does a smart trip-wire device (eyes on a garage door opener) exist?

Hello, I’m new here and apologize if this is an inappropriate question for the forum. If it’s appropriate, I was wondering if there existed an openhab capable outdoor trip-wire device. Essentially garage door eyes hooked up to openhab to tell me when the beam is interrupted.

For use case description this would be used at my home to alert me of a vehicle entering the driveway. Set at the appropriate height it would not detect animals and only detect humans and cars.

I partially considered hacking something together if nothing existed but I would struggle and it would be time consuming.

Many apologies if this is not an appropriate post/location. This is my first post, be gentle :wink:

Treat as two requirements ;

an outdoor break-beam as used n any number of security systems (commercial products are not cheap but very effective)

a means to communicate back to openHAB server.

Wired? Wireless?
Distance to cover for sensing?
Distance to cover for reporting back?
Existing technologies in use?
Power available at one or both ends? (Reflector beams exist but are not as effective)
Alternatives? (outdoor PIR are not very good at cars, from experience.)


In addition to the questions @rossko57 asked, how wedded are you to this specific idea of a break-beam system? There are lots of battery-powered outdoor motion sensors that could handle your notification requirements with ease, and you might be able to position one so that it doesn’t pick up small animals. You could even build an enclosure that limits the sensor’s field of view to a specific area (while also protecting the device from weather).

I will report practical experience of purpose built (wired) PIR sensors, intended for the 15m - 20m range. Both expensive 200 quid types, and cheaper chinese 20 quid copies.

Really good for pedestrians, in summer or snow or rain, I would say 95% reliable when aimed properly to avoid coverage gaps. With two sensors, entirely trustworthy… for pedestrians.

Can be set up off by rabbits and foxes and owls (we’re remote enough not even the farm cats stop by), especially when bunnies are frisky and run about. Harvest moon for false alarms, every year.

Can be set off by waving vegetation in field of view in right circumstances. Smarter PIRs try to tune out background noise, but this will never account for a sudden squall.
This is the apparent cause of our pedestrian “misses” - on a wild windy day, the auto desensitizing means it can miss a real target.
Only an issue if the field of view includes vegetation, obvs.

Can be blinded by direct sunlight into lens - choose position carefully.

Hit and miss for vehicles. Down to 30% success rate for fast moving vehicles (fast in this context, about 15mph, the target zone is a narrow gateway) on a rainy day. (my personal theory is PIR are most likely to trigger off the exhaust plume, which is smothered by cold rain and dispersed by speed - I have no experience of electric/hybrid targets but would expect rubbish results)

Microwave motion sensors should fare better here, no experience.

Compare to -

Infrared beams of reasonable quality (where the IR beam is encoded, not just light) -100% reliable and precise. Nuisance to install due to siting and wiring both ends - once.
Can in theory be set off by leaping foxes, cats or swooping owls - never happened yet to me.

For added confidence, I saw an army ammunition store upgrade its perimeter sensing just three years ago. I would imagine that is a “no expense spared” kind of job. They used these -

These are NOT the same, but at one tenth the cost they work well

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This paragraph made my day.

Interesting that it doesn’t pick up vehicles reliably, since there are so many heat sources (engine bay, wheels, and exhaust in particular). Perhaps electric cars with individual motors at all four wheels will have brighter heat signatures/profiles?

The eBay sensor barriers you linked are interesting from a cost/performance perspective. I like how it uses the dual beam to differentiate between humans and small animals. Not the prettiest devices to mount at your entrance, but there are always trade-offs.

Give it some thought. These break-beam black bricks have installation disadvantages, but I repeat, are precise and reliable in operation,

Vulnerable - you can’t (usually) mount out of reach. Breakage or tampering is rewarded with a trigger of course, but it is difficult to mount where they cannot be smashed maliciously. Sneakiness, uhh, discretion is more effective than ridiculously armoured boxes.
(The army job just left them exposed; whether you step through or smash one up the result is the same, arrest by MPs. But they’re not worried about casual vandals and replacement costs.)

Example, covering a gateway? Mount on inside face of gateposts, not visible from outside. Or exploit the range, mount on next fencepost along from each gatepost. Or on posts hidden in the hedge further up the drive. Or go diagonally somewhere, you don’t have to do the obvious straight across.

Power consumption is modest, battery operation a possibility, but both ends need power. if possible, linking transmitter and receiver ends by wire simplifies your battery management.

Rossko57, I am open to (and appreciate the analytical approach of) separating into 2 requirements.

  1. The break beam
  2. Communication medium

To answer your questions on 2:

I specifically installed a wireless AP just outside the window facing the area for this reason however in full disclosure I am completely open to a wired connection for it’s robustness considering my use case is to keep myself and family safe. I happen to be an agile developer and would like to iteratively improve the solution if possible starting with wireless for MVP and progressing to wired someday.

Sensor distance: 20’ / 6m
Report back distance: 150’ / 45m
Existing tech: This would be my 1st openhab integration

Power available at both ends: No, and yes. There are two light fixtures on the pillars I’d like to sensor. However they’re switched and only on at night and rarely. However I could probably utilize some HA tricks to wire them on constantly but install smart bulbs and switch THOSE off. So no, but possible through some trickery.

Alternatives - I am completely open to any solution with the most reliablilty and least false positives. The true concern is knowing as soon as possible when someone is entering my property. The less I know about the twitterpation of the local fauna the better as it will train me to ignore the warning if there are too many false positives.

I actually started this journey by considering security cams but they had just far too many false positive reports for me to take them seriously.

Rpwong I believe this answers your question of how open I am - very. I defer to others experiences and greatly appreciate both of your feedback. I have never considered narrowing the field of view of a motion sensor and I was completely oblivious to the plethora of information rossko just bestowed upon me. I am still going over it all to piece it together.

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Out of my area … but if you have existing mains wiring to your gateposts, I’d look to exploit that.
Mains carried switching control for your lights and mains carried signalling for the sensor? I know nothing about this but sounds like a job for “powerline relays” or whatever the terminology is, in both directions. Oh, and a little bitty 12V supply for the beam.

There are ways to do this with cameras, I have setup a way that is running for 6 months now and I have only had 1 single false positive out of the hundreds of times it worked flawlessly. The trick is to use multiple sensors that have to agree before the event occurs. Each method may have false positives, but when combined they almost eliminate the issue.

You can get cameras that have built in PIR that need to see heat and movement, then they also have the ability to use the cameras picture to determine the size of the movement as a percentage of the size of the screen. Some cameras have trip wire and other smart alarms. These get fed back to openhab and you can use them in rules for logic, but you have to have the right mind set to get this kind of thing working.

There are now also methods of using computer learning to detect if the movement came from a bird or a human. So there are multiple ways to achieve the same goal each with pros and cons. A few people have posted about doing this on the forum as when only processing 1 frame every second this can run on a dedicated raspberry Pi. Compute sticks can also be used to offload the processing power as well.

@matt1 I would like to think as a passionate software developer at heart I have the right mindset. I have no problems putting forth effort to solve the problem.

I like the concept of having an array of devices that need to agree on input to make a decision on threat detection. Since you’ve solved this problem so effectively already (I would find 1 false positive per month acceptable so you’ve greatly exceeded my acceptance criteria) would you be willing to make camera recommendations based on your experience?

You mentioned the ability of getting “percent of area moving comparative to field of view”. Is this value provided by the camera software itself or did you have to roll custom image processing software yourself to do this? I’ve done image processing logic before but that was 15 hears ago and I’m quite rusty. It would take me considerable time to roll that myself and would prefer to leverage something pre existing if at all possible. Work smarter not harder type thing.

Thank you so much for everyone’s feedback! This community is GREAT!

You will be fine, maybe half a day of tweaking and it would be setup. I just would not recommend it to someone that needs their hand held as it takes time to tweak each alarm with the end goal in mind for when they are combined. And if you need different settings at night VS daytime, it can be ‘fun’ to get right.

Yes it is done on the camera so next to no CPU load on your server, you just use a Openhab rule to combine the separate alarms. Hikvision cameras allow you to specify the size that needs to trigger the alarm. It is not user friendly as if you use multiple AREAS to ignore movement from trees then you have to specify a % based on each individual area, not based on the total pixel of the camera. Hard to explain but there are youtube videos that shows the features as well as the manual.

The smart alarms are great especially the line crossing alarm (dahua call it trip wire alarm) these are known to seriously reduce false positives and in the case of Hikvision it can tell me if the movement is towards my house or away from my house, this decreases the false positives yet again. I don’t get push alerts when I leave the house, but when I or anyone else comes home I do. Of course the cameras are recording independently of Openhab using different rules to my push alerts.

The problem is you need to combine multiple alarms from the camera because the standard movement alarm can detect size, but the line crossing can not. So when the line is crossed I check the normal motion alarm and this tells me if it was a bird or a person based on if the size tripped the second alarm. You can then combine with other sensors not in the cameras like PIR.

Instar cameras have a cool feature where you can tell the motion alarm not to trigger if the built in PIR does not agree. This is done at a camera level which may work better at stopping recordings from occurring as the Hikvision can not combine the alarms and the more you turn on the more it records.

Each brand is different and good for a different situation.

Welcome to the OpenHAB community Russ.This forum is a great place to start this discussion and as you can see a lot of us find it an interesting subject. Everyone’s experiences with motion sensors is helpful even in an indoor context as well.