Door Alarm

Keep forgetting things when you walk out your house? I did all the time, before I made this handy door alarm to remind me. This small device solves that problem, while staying discreet right until you open your door. It is attached and functioning with little setup, and is completely customizable.

This project will require some basic coding and wiring knowledge, but is overwise pretty simple. Because everyone's doors are different dimensions, keep in mind that you will have to adjust some of the steps to make sure it works for your unique home - I will make it very clear which measurements you will need to change. Without further ado, follow along to build this small and handy device!

The most important things that you will need are a Circuit Playground (I used the Classic) and the battery for it. Find these items here.

The other supplies you will need are:

• A box at least 3" x 3" x 1". Make sure the box is still small enough to fit behind your door when opened.
• Two thin copper plates, no thicker than 1/4 cm. I found mine at Lowes for about $10 each.
• Tin snips. Must be able to cut through sheet metal. I got mine at Walmart for $16.
• Duct Tape. I got a roll at Walmart as well for $4.
• Four double ended alligator clip cables. Order them online here for $6 a pair.
• One external LED light. I used the ones similar to those in this set.
• Thin paper. I used tissues but you could use wax paper or similar items as well.
• Scissors/box cutter. Anything you have that can cut cardboard works.
• Command Velcro Strips. Once again, I found these at Walmart for about $10.
• A Sharpie. If you don't own one you can find one at Walmart for cheap.

Here is the basic blueprint I used for my alarm. The red square is the box that your circuit playground and battery will sit in, attached to the door frame on the same side as the hinges. This is where you will have to measure your door to make sure your box fits properly. The two blue lines in the top right are the two copper plates in between the door and the frame. Once again, you will have to measure your own door to make yours fit perfectly - you may need to add more duct tape to make sure the plates are touching when the door is closed. The alarm only functions if the plates touch, since they are what completes the circuit. The black box is the battery, and the other orange lines connect to the LED which is also housed inside the box.

The code for this is pretty simple. This alarm works by activating when a circuit is broken and the door is open, and the alarm is silent when the copper plates are touching and the door is closed. Make sure you have access to at least two pins and two grounds, since you will need all four for the alarm to function properly . Make sure you attach your external LED light to the pin specified in your code. You can customize the colors and sounds as much as you would like!

A common problem here is mixing up your pins, so just keep them consistent. Labeling them out on paper in an easy way to keep track of which pin connects to which.

Here you will have to set up your Circuit Playground, battery, and LED light so that they all fit inside your box and are properly connected to one another. I used duct tape to hold them in place. Make sure the alligator clips don't touch metal to metal, since that will short the whole thing out. A common problem here is your wires getting all messy - I used small strips of tape to coil the wires into small circles before attaching them. I used a box with a lid so that it would be easy to open and close to access the wiring.

You need to cut holes in the side of the box large enough for the alligator clips to fit through, since they will be connecting externally to the copper plates you position between the door and the frame. I used scissors and a box cutter to do this, but you could use anything.

For the copper plates, you will have to do some more measuring. The plate's width should be same as the width of your actual door - this way they will fit perfectly into the gap between it and the frame. Make sure to include small section that jut out so that the alligator clips can attach well. Having the two bumped out sections of copper a few inches away is an easy way to avoid them touching once they are in place. You can also test the alarm here since it should be fully functioning at this point - all that's left is add the windows and to get it in place.

Here is where you cut out the windows to display your LED light and preferred reminder message. I taped tissue paper to the inside of the box and wrote on the outside with a sharpie, but you could use any semi-transparent material here. A common problem is that the lights from your circuit playground and your external LED light blend together visually - I added a small cardboard separator taped to the lid in between them to fix this issue. Make sure to measure all of the holes beforehand, so that your message will fit. Then attach the Command Velcro strips to the back of the alarm box.

This is the final step before your alarm should be fully functional. Once again, use the Command strips to attach the alarm box to the wall next to the door, making sure the door still fully opens without crushing it. Then, use duct tape to attach the copper plates to the inside of the door and the door frame. Be careful not to cut yourself, as I did when I set mine up.

A common problem is your copper plates not having a good enough connection. Make sure the copper faces of each plate fully touch when the door is closed. Add more duct tape to either side if they don't. Make sure the door is open when you turn on the battery, otherwise it breaks for some reason. After that, you are good to go.

Congratulations! Your alarm box should be fully functional and attached right where you want it. Feel free to customize the look, shape, and message on the box as much as you like. I hope it is as useful to you as it was for me. If you need a more in depth video look into how it is supposed to function, you can find that here.