Out of range sensors

Hello, I am new to the forums and arduino. I am working on a project and would like to know if there is a way to set a sensor to send a text to my phone when I step out of range(about 5ft).

Thank you

What do you want to detect, presence/abscence of just you, or any person?

MarkT thank you for your reply.

I would like to detect absence. If I walk away from the "base" it would alert me that I am not near the base anymore. Does that make sense?

The question remains: absence of what, exactly? Just you, or any person? If just you, how could the sensor possibly identify you and distinguish you from other people? How exact should that distance be? From any part of your body or a specific point of your body? (the range of 5 ft is less than the length of a typical person).

The moment you have that part settled, the sending of an SMS becomes quite trivial in comparison.

Ok here is an example of what I am trying to do. Let's say I have my book on the table with the Arduino connected to it and I have my phone connected via Bluetooth. Is there a way to have a text alert sent to me if I walk 5ft away from the book? And what products would I need to purchase to make that work?

Do you assume you have your phone on your body? In other words: you try to detect that your phone is 5ft away from the Arduino, rather than you yourself?

Yes if I have my phone on me and the detection is between the phone and the arduino.

Or is there a transmitter and receiver that can be programmed to detect that they are 5ft from each other?

shepalep2432: Or is there a transmitter and receiver that can be programmed to detect that they are 5ft from each other?

There is, not tried them myself;


The easy way: Bluetooth out of range (a tad more than 5 ft unless there's a wall in between).

The more accurate way (don't know if a phone can handle this): combination of ultrasound and a radio or IR signal. The time difference between the arrival at the other end gives the distance between the two: sound is much slower than light.

The modern UWB time-of-flight sensors are supposed to be accurate enough to do this - loss of signal is a very rough guide to distance by comparison as RF signal strength is highly variable. But even UWB needs a reasonable line-of-sight path I believe.