Here's a great way to always check whether or not you locked the deadbolt in the door or if the garage door may be open. Super simple to make and cheap.
LED (any colour)
Resistor to match LED (http://ledz.com/?p=zz.led.resistor.calculator)
Old Cellphone Charger (5.0V)
2 x 1k Resistors
NO Magnetic Proximity Switch (http://www.abra-electronics.com/products/-SPST-Magnetic-Proximity-Switch.html)
NO Reed Sensor
NOR IC (74LS02N) (Datasheet: http://www.datasheetcatalog.org/datasheets/70/232221_DS.pdf )
Hot Glue Gun
Begin by thinking about how you will want to wire everything. When I did mine, it made the most sense to go right across the ceiling and along the baseboards. Your will probably need ~100 ft of wire. Look at the wiring diagram and make sure you understand what needs to go where.
Do a rough job at first and place the components where you need them to go.
J1 and J2 in the schematic are the NO magnetic switches.
Screw the Magnetic Proximity Switch into the wall and onto the side of the garage door. Make sure that when installing it, the switch does not interfere with the opening and closing of the garage door. It may take a while to find the perfect spot.
To install the reed switch, you will have to take apart the door frame and possibly the wall. Not a difficult task, just time consuming.
Use an old phone charger to power the circuit. Phone chargers convert AC into DC and are usually around 5V. It's important to use a charger that is exactly 5V because the NOR chip needs 5V to be powered. To get the positive and negative terminals of the power supply, simply cut off the tip that normally connects to the phone. There will be a red (positive) and a black (negative) wire.
You can choose any colour LED you want for this project. All you need to do is find a suitable resistor so that the LED is running at it's rated current. Use the link (http://ledz.com/?p=zz.led.resistor.calculator) and plug in 5V for the supply voltage. For the current and voltage drop see: http://www.oksolar.com/led/led_color_chart.htm
If you get a clear LED like I did, you can make it have a diffuse look to it but lightly rubbing it with sandpaper.
Also place the LED inside the house so that whenever you're walking by, you'll be able to see if something needs to be locked or closed. For this you'll need to drill through the walls like I did. Also drill a small hole into a light switch cover to give it a nice finished look.
**Note the polarity of the LED. When the output of the IC is low, it will make the LED turn on. Do reverse it!
Now solder all the wired to the resistors and cover everything with shrink wrap. The final step is to connect all the wires to the integrated chip (NOR). See the wiring diagram in step 1 and also the datasheet in the intro. Solder on all the wires. Be very careful with the pins on the chip as they are very delicate. If you don't have a little box to put the circuit in, you can do what I did and saw off the top off a plastic cap on a spray paint bottle. This can be used as a seal to prevent dirt and water on the circuit. Seal it to a wall using hot glue.
Done! Go check if it's working, if not troubleshoot with a multimeter. Don't forget any resistors otherwise you'll burn something by causing a short.
Hope you enjoyed my first instructable. Next time I'll make it step by step instead of showing the final product. Any comments would be appreciated.