by ronnietucker @ instructables.com:
So, first thing I did was to get the LCD and keypad working together.
For this I pretended that it was some sort of arm/disarm (or entry/exit) thing.
My code for this part is at: http://pastebin.com/YndLneqm.
Getting the LCD wired up was tricky as most wiring diagrams for it don’t show the last two pins wired up and these are required for the back light. Check my snazzy Fritzing wiring diagram to see how I wired up my LCD screen, pot (for adjusting brightness) and keypad. The pins for them all are also mentioned in my code.
Arduino Laser Trip Wire - [Link]
by micahmelnyk @ instructables.com:
In short: I developed a portable, battery powered device that sounds an alarm when your bag or purse is moved. Once armed, can only be turned off by your secret code.
The device is built off an Arduino compatible Trinket Pro, using an off-the-shelf project box with PCB.
Bag movement alarm for theft prevention - [Link]
by Joe @ hobbyelectronics.net:
This project was built to monitor the temperature of one of our computer rooms at work that has rather temperamental air-conditioning. The maximum temperature can be set, and if this is exceeded an alarm is activated.The unit gives a continuous display of current temperature and it’s possible for the constructor to change the device program firmware or display board.
LED display Over Temperature Alarm - [Link]
This is a website down alarm using a Tessel module. Check it on projects.tessel.io:
If your website goes down, you want to be the first to know. Make it obvious when there’s a problem by hooking up a big alarm light to a Tessel, which will ping your website every few seconds to check for trouble.
Continuously off: all is well
Continuously on: website being monitored is down
Two-second bursts (on or off): system error; monitoring isn’t working (reset the Tessel)
Website Down Alarm using Tessel board - [Link]
by DIY Hacks and How Tos @ instructables.com:
Winter is coming. So it is time to make preparations. If you live in a colder climate, you need to be concerned about the possibility of your pipes freezing. There are a lot of preventative measures that you can take such as insulating your pipes and leaving the water dripping. But for a little extra peace of mind, I designed a simple alarm that will notify me if the pipes are getting too cold and are in danger of freezing.
Frozen Pipe Alarm - [Link]
Water Level Alarm is a simple project to detect and alarm once the water level in tank or Aquarium reaches at certain level. Circuit is based on popular NPN transistor BC547 which act as switch, Sensor also made on PCB, when the water reaches the sensor PCB, base of transistor connected to positive supply, in consequence transistor act as switch and activate the buzzer.
Water Level Alarm - [Link]
by Martin @ harizanov.com:
I purchased a battery operated smoke/fire alarm few days ago and it showed up today. It runs on 9V and will make a loud sound if smoke is detected. My intention was to hook it up with my home automation system so that I would receive alert if it would go off including SMS, pushbullet notification to my phone, email etc.
The Funky v1 is ideal for the purpose because it is really flat/tiny and would fit inside the alarm. It will tap into the piezo siren and sleep until the siren is activated. Upon activation, it will make a wireless transmission to my home automation system (Raspberry Pi running Node-Red) for further processing and alerting me on my phone.
DIY Internet of Things Fire Alarm - [Link]
This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1.
The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its reset pin becomes high. When the Laser / IR beam breaks, current through the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.
A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.
555 Photodiode alarm - [Link]
Markus Gritsch build another bedside table alarm clock, the schematic and source code is available here:
recently some vintage bubble displays popped up at various places , so I felt the urge to build another bedside table alarm clock, this time a really tiny one, roughly the size of an AAA battery.
Bubble display alarm clock - [Link]
hertzgamma @ instructables.com writes:
This instructables will show you how to make an alarm system that will beep a buzzer if you leave the fridge door opened for a long time to remind to you to close the door. All new fridges on the market have this option built in, but some may want to upgrade their old fridges.
Fridge Door Detector Alarm - [Link]