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My project is to build a raspberry based emergency button for use at home (if someone feels unwell, for example).

I would like to use the raspberry pi as a receiver of a signal sent by a (short-range?) radio transmitter (on a press of the button) for further processing. I imagine it would be similar to how car remote key entry systems work.

I have a hard time figuring out what hardware to use as the sender and the receiver. Many articles I found are about FM radio but I think that is not what I need, or is it?

Hope someone can give me a step-by-guide on how to go about this, hopefully including some information what hardware exactly I need.

Thanks very much!

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Another option would be to buy a transmitter and receiver pair. Modules are commonly available for 433MHz.

For example: http://shop.ninjablocks.com/blogs/how-to/7506204-adding-433-to-your-raspberry-pi

Now that tutorial shows sending of id numbers over the 433MHz link (using on off keying) - in your case you only need to see if the button had been pressed, so reading the gpio directly should do that.

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If you want a simple solution that has a button on the transmitter and a LED/buzzer/speaker on the receiver you do not need a RPi at all. Just build a simple RF transmitter like this one: Simple RF Receiver / Transmitter Pair (27 MHz).

Of course, If you want a more sophisticated action on the receiver side (like connect to LAN etc.) you can connect RPi to the 27 MHz receiver and read its signal via GPIO input on the Pi.

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For maximal coherence-resistanse I do recommend you to use a Bluetooth. On Raspberry side use an USB dongle, I prefer ASUS ones or Bluetake : best range. On "button" side use Arduino+BT shield, or Bleduino(it's an Arduino + BT in one board), here is the site. After that it's just a standard classy tasks like arduino button and bluetooth serial port communication. Take a look here

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  • Thank you! I have not thought about BT.. and I can see your point about coherence. I have browsed some more and I am thinking of maybe generating some unique audio sequence and capture it via voice input with this device: makeuseof.com/tag/… – Marc Jan 31 '16 at 18:49
  • @Marc it will be VERY unreliable, use any digital radio protocol - my good advice to you. – Alexey Vesnin Jan 31 '16 at 19:29

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