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Comment by impostervt | Hacker News Reader

I'm interested in making a door movement sensor with a remote alarm to wake me up if my sleepwalking daughter goes roaming.

As a software person who is just getting into electronics (played with a particle photon, just bought the Make: Electronics book & component kit to learn), what are the options when you want to have two pieces of hardware communicate inside a house?

- Bluetooth - limited range?

- Wifi - requires you to join each piece to the network, seems a hassle/expensive for simple electronics.

- Xbee - expensive!

- RF transmitter/receiver - seems cheap, but maybe distance is limited and there may be a lot of noise?

Anything else?

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Look up the ESP8266. It's a very cheap piece of hardware that you can program using the Arduino IDE. It can connect to your local WiFi easily and send a push notification to your phone.

So you can build something like this using a simple PIR sensor + ESP8266.

Just made an account to say this and you beat me to it.

I built a garage door opening sensor using an ESP8266 (connected to my home wifi) and a magnetic contact switch. I'm also using TelAPI to send me SMS messages every time the garage door is opened.

It is very simple to do, and kind of cheap.

Could you please share any existing sources (schema, firmware)? Thanks in advance.

Thanks, sounds similar to the particle photon + pir sensor I used for my version 1. It works, but i'm wondering if the phone part is overkill if I want to make this into a real product. Requires programming, an app on the app store, etc. If i have a second piece of hardware to receive and make noise, maybe that would be easier.

You didn't mention wires. And I think it's worth considering. Most probably your sensor is going to be connected to power plug (if it goes detached). So why not to situate mini-server (RPi-alike) nearby, with a sensor connected by wire?

Not sure I follow. The door sensor is going to be hanging on my daughter's door, and the alarm would be in my room, probably 40 ft away.

Wherever you place the sensor, it most probably needs power supply. Batteries die, so I'd go with plugging into power socket. Since we use a nearby (to daughter's door) power socket, we could insert _right_there_ a mini-PC to control the sensor (because sensor just senses, and you need some "digital brain" to do something with results of sensing). Then mini-PC could notify you in a lot of possible ways.

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