If you're reading this Instructable, you may probally be tired to find your pets walking outside every night. That's why I came up with this design about a compact tracker which will allow you to find your puppies/kitties outside easily.

You just need to send a SMS to your pets, an alarm will be triped, then you can find them in the darkness by following the sound.

I try to make it as compact as I can in order to fit every pets.

Step 1: Supplies

This device is made by a microcontroller.

Therefore, you will need :

An arduino Nano/mini
A small Lipo battery (3.7V)
A buzzer
2 resistors (10k and 20k)

You will need a bit soldering skills to solder everything on a prototyping card.

Let's code

Step 2: The Firmware

The code on Arduino is not too long. We only need to read and make AT commands, and then the protocol will communicate itself with the GSM shield.

Thus, I make a whitelist with phone number which allows you to find your pets. As well, I make a case that allows you to send a specific message to your pets, then the alarm will show you the place of them.

But verything is commented in the code, so you can't make mistakes. Let me know if you have any problem in the comment section.

Kitty_finder.ino
Download

Step 3: The Hardware

Firstly, upload the sketch on the board. Once everything is ready, unplug the USB cable.
Then you can weld everything according to the schematic.
The battery will be used to power the Arduino and the SIM shield. Is very important and necessary to use a battery because the shield can appeal a lot of current.

Two resistors are used to decrease the amplitude of the command.

Then weld the buzzer to an analogpin in order to have more current while making the buzzer ring.

Step 4: Understand the SIM800L Shield

Once you power the shield you will see a led blinking. There are 3 modes

One blink every 1 second
- No network
One blink every 2 seconds
- GPRS data active
One blink every 3 seconds
- Ready to work

Generally you will see the led blinking every second, move a bit and orientate the antenna away from metal pieces.

Then wait a bit of moment and it will work normally.

Step 5: Final Test

I made a small cover and sold everything in.
I put this on my teddy bear because I don't have my cat around me. I asked my friend to hide it in the flat and I find it successfully.
The buzzer was loud enough even hearing from the outside, that was really impressive.

Step 6: What's Next ?

I've noticed that using a SIM card to find a pet is not really confortable. I will now investigate on how to use a LORA system. But I didn't manage to find compact design yet.