Drentsoft Doorbell Early Warning System Improved Doorbell Responsiveness

What is The Drentsoft Doorbell Early Warning System?

Drentsoft Doorbell Early Warning System is a hardware/software system for determining both when to answer the doorbell and knowing when the postman's arrived with your precious postal goodies.


There are times when you just don't want to answer the door for whatever reason be it you're in the middle of something, you're not feeling well, you think it'll be a waste of your time etc. With the Drentsoft Doorbell Early Warning System you can decide ahead of time whether the person approaching the door is worth your time and effort. Think of it like a predictive intercom without the interaction.

That seems a bit mean I hear you say

Yes and no. Put it this way, think of your poor grandparents, knees aching, they spend all their time upstairs where the house is warmest. Someone rings the doorbell and by the time they've managed to creak their way downstairs the ringer has got bored and left r maybe they're some overly aggressive door to door salesperson who won't take no for an answer.

Now imagine if they'd had a system like this where an image of the person is sent to the nearest computer and they can decide whether it's worth their effort.

Old people with on-hand technology? That seems a little unlikely...

This might seem a little far-fetched as retirees are probably the least likely demographic to be sat next to a computer/smart device when their doorbell is rung but it's not beyond the realm of possibility. Smartphones are making people more and more interconnected and many grandparents are being setup with smartphones so they can perform VOIP calls with their distant relatives, live and with video. Why couldn't they install an app on their phone that improves their lives even more.

I'm still not convinced. I want at least 2 more suggested uses

OK, not satisfied? What about these.

  1. You're waiting desperately for the postman to deliver your latest prized possession but he often doesn't deliver at the same time every day. If you're upstairs you'd be running up and down all morning/afternoon or straining your poor ears waiting for the sweet sound of "droppage".

    Or not, you're busy working at your desk when a window pops up and WOW! It's the postman!
    You've now freed up your morning for useful work and still have the delight of picking up freshly delivered goodies.

    Disclaimer: OK, this might not be that useful for everyone but as someone self-employed who mostly works from home it's a really serious issue!!


  1. Reduce unnecessary trips to the door to see if post has been delivered
  2. Reduce wasted trips to the door for people who would waste your time (cold calling/non-supported charities/gas tarriff offerers)
  3. Know ahead of time that someone's about to ring your doorbell so that during times when you might not be able to reach the door quickly you have a headstart
  4. Point 3 is especially useful if you have a hard to find and/or temperamental doorbell


Client computers/phones/tablets connect to a network/internet enabled Raspberry Pi server.

PIR motion sensor triggers the Raspberry Pi camera module, taking a few snapshots of the approaching doorbell ringer.

The Raspberry Pi, being connected to your network (and possibly DNS'd to the greater internet) sends the images to all connected clients.

The clients receive the images and can quickly decide what to do about the person at the door (ignore/run down etc)

Potential Issues

The biggest issue at the moment is how to power the Pi.

  1. The first option is to just drill through the brick wall, run a USB cable from the Pi to the power socket near the front door but this is a bit annoying and while heat loss isn't too much of an issue as the porch will protect against the majority of the heat leakage it would be problematic for anyone else using a similar setup.
  2. Another option is to just run the cable between the door and door frame but while these USB cables are pretty thin, there's a potential for the cable to get seriously snagged. There's also the potential for someone carrying too much shopping or a heavy toolbox to yank the cable out of the pi or power socket. A work around to this (snagging by passersby, not the door pinching) would be use a much longer cable, route it up the wall to the top corner of the door and then back down the wall to the power socket but as I understand the maximum length for USB data is 5m and if power is similarly affected it would seriously limit the placement of the pi without the use of an additional extension cable.
  3. Another option is to go battery powered but depending on capacity this would need disconnecting and recharging about once every day or two which short of having 2 batteries on the go at any time would require a lot of work to keep maintained and involve a lot of downtime which might render the whole project moot if more doorbell calls are missed due to a lack of a running battery.

  4. A mixture of battery and solar power might work quite well but would double or triple the cost of the build.
  5. Wireless power would be cool but is obviously impractical at the moment given that it would have to get through several centimetres of brick and would be rather expensive to implement.

Parts List

  1. Raspberry Pi Model A or B (A recommended, it uses less power)
  2. Some kind of waterproof housing for the pi. If the project will be in a weatherproof porch or under an overhang away from wind and rain a regular pi case with screw mountings may work.
  3. Raspberry Pi Camera Module
  4. USB wifi adapter
  5. 4GB+ SD card
    • Class 6 or higher for quick booting and image IO
  6. PIR Sensor
    • Preferably can run at 3V3 or lower
    • Preferably outputs no more than 3V3
    • Preferably minimum sensing range of 5m to give the maximum warning
    • As wide angle as possible so you can detect people who approach from angles you hadn't anticipated


Disclaimer: All prices are approximate and are subject to change by the various suppliers.

Worst case: £60

Best case: £42

These may seem a little steep but first off the Pi will be connected to your network so you could always SSH into it and do other cool things when you don't think you'll need the doorbell monitor. You could also only mount it on days when you're expecting a high level of footfall, for example days when you're expecting a workman or on a day that you've taken off work to wait in for a delivery.

My Chosen Parts

As this is still very much an experimental concept at the moment I shall be using a model B Raspberry Pi that I can use for other purposes if this project doesn't work out. The idea being that I can always switch to a lower powered model A if I decide to make this a permanent setup.

I have a porch between my front door and the doorbell so for my purposes any old case will do as long as I can find some way of mounting the case to the brick outer wall. I'm tempted to go for the Cyntech case sold by Mod My Pi for £6.99 as it has screw mounting holes on the underside.

The Raspberry Pi camera module is basically a given, one could maybe use a USB webcam but it would require the use of a model B for the 2 USB ports or a powered USB hub, which would make the power situation that much more complicated again.

I think the Tandy PIR sensor makes the most sense as it outputs the correct voltage for the Raspberry Pi GPIO and accepts input voltages that the Pi can supply and at £3.99 + £1 postage (at time of writing) this seems reasonable especially weighing up the delivery times for the eBay ones.

Optional Extensions

The Raspberry Pi server could also connected to an LCD near the doorbell, a receiving client can then send one of several messages such as:

The LCD can also be used to tell the person at the door about the doorbell position if it's hard to find

The LCD could be combined with a couple of flashing LEDs to draw attention to it

For a fun coding exercise, get rid of the need for the PIR and use the camera itself as the motion detecting sensor.

PIR Update - 2013-05-28

Upon further research I have discovered the most PIR sensors won't be able to penetrate glass. I had assumed that most household alarm motion sensors simply didn't pick up on motion through windows because they were designed to have a range that was just long enough for the average sized room with the majority of the power dissipating against the window.

What Does This Mean For the Project?

For most people who would mount their doorbell monitor outside, not a whole lot but I had planned on mounting everything inside the porch, a mostly glass structure. This leaves me with 3 options.

  1. I believe there are motion sensors that work on microwaves rather than IR which allows them to penetrate through glass. I also suspect that these are out of the budget range for this project
  2. Mount the PIR sensor outside. This isn't an entirely appealing prospect as I would have to:
    1. Run the cable through the letterbox in a way that it wouldn't interfer with post
    2. Run the cable between the door and doorframe
    3. Drill 1 hole through the PVC frame of the porch
    4. Drill 2 holes through the brick either side of the PVC and pass the cable through these.
  3. Use the camera along with some computer vision software to determine if and/or when someone is walking onto the drive.
For the time being I think I'll stick with experimenting with the PIR sensor, it's rather cheap and I can always re-task it to something else if I find it's not suitable. If it turns out not to be I shall start looking some simple computer vision algorithms.


I hope I've at least given someone some sort of inspiration for projects that could be done with the Raspberry Pi even if they think this design is too expensive to be of any practical use. I've had another idea for a web enabled security camera using the Pi and the camera module that takes pictures of hooligans if they stay near the house causing problems too long. More on this on its own page soon.

If you liked this project, why not buy me a beverage?

App Appreciation: Usefulness