# Simple wireless transmitter for notification when circuit turned on

I have a simple home project I'd like to implement. Being a electronics newbie I'm not sure exactly how to go about it.

Basically, I'd like to build a device that is attached to a (12V) power supply line that simply sends a wireless signal/alert to my smart phone when the power is turned on i.e. current running through the wire.

The signal only needs to be transmitted roughly 1-3m, so I assume some sort of Bluetooth transmitter spliced into, and piggybacking off the power running through the 12V wire will suffice? The device does not need to receive signals i.e. one-way communication only.

• Thanks guys. I realize now my initial post was lacking a little detail - newbie to electronics and forums. Anyway, the application will likely be outside, with no wifi, and at times no data/internet of any kind. Furthermore, I would prefer a relatively "hands free" notification solution e.g. phone simple vibrates, emits a sound etc. As such a solution via email would be unsuitable (but thanks for the advise anyway). I assume therefore that the BLE chip/board is perhaps the right way to go. I'll take a look. Thx. – James Jul 14 '17 at 11:58

I would suggest using a Raspberry Pi with a wifi board. Feed the voltage (after regulating to 3.3 V) to a GPIO pin. Monitor the pin, and send yourself an email when it triggers.

Alternatively, power it directly from the 12 V so that it is off until it's needed. Have the message sent automatically after boot. Then you can program it to shutdown.

• ESP8266 would be far cheaper, and doesn't need to be on all the time. – cranphin Jul 14 '17 at 8:23
• @cranphin probably right. I posted this before the other answer. Still this would have way more capabilities, should the need arise. A PI is maybe $10-$30 bucks. Not too bad. – Blair Fonville Jul 14 '17 at 8:27
• @cranphin Updated the answer. This doesn't need to be on all the time either. – Blair Fonville Jul 14 '17 at 8:34

If you have WiFi then use an ESP8266: -

You'll need a power supply and you'll need to be able to put some firmware into it.

Anyway, the application will likely be outside, with no wifi, and at times no data/internet of any kind.

Then there is the ESP32S combined blue-tooth and WiFi module: -

There are quite a few options for blue-tooth/WiFi

I suggest you to try NRF51 based boards. which is cheaper and uses BLE to communicate.