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The simplest cheapest cheapest gsm notification of motion detection. PIR + Telep

Tomasz_72  2 9270 Cool? (+4)
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TL;DR

  • DIY GSM motion notifier pairs an old mobile phone with a PIR sensor and a photoresistor, with no Arduino or microcontroller.
  • The PIR lights an LED that illuminates a photoresistor soldered across a phone key, simulating a long press to dial a preset number.
  • The builder used a Siemens S55, powered the setup from 3.3V to 5V, and limited LED current with a 500ohm resistor to 10...15mA.
  • When motion is detected, the phone interprets the changed resistance as a button press and calls the selected number.
  • It only works on phones that can dial by long press without green-handset confirmation; the original phone battery was replaced with an 18650 cell.
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What is it and how did it start

Recently I did an alarm with a gsm notification. But the alarm itself communicated with the phone via a serial connector, providing number identification and specific information sent by SMS. However, in many cases, the details of motion detection are irrelevant. It is important that we get an immediate notification on the phone that the sensor has detected movement. So I came up with a method of implementing this idea based only on the old gsm telephone and motion sensor. No Arduino, no microcontroller!

What is the idea?
However, the telephone used must have a specific function: a long press on the key dials the number. WITHOUT green phone confirmation. My siemens s55 can do it. Thanks to this, we can directly from the motion sensor send an impulse "pressing" a specific key on the phone
and dial the number. To make the system more universal, I soldered a photoresistor instead of a key on the phone. If it's dark, it doesn't do anything, it's (almost) a break. If the sensor detects motion, it will light up a diode that illuminates the photoresistor causing (almost) a short circuit which the phone will recognize as pressing the button
How to build a layout?
First get a phone that dials one-touch number without confirmation with the green handset. Then "program" the number the phone will ring during an alarm. The system (sensor and telephone) needs 3.3V to 5V for operation, but will work more stable if it is powered by a battery. The one from my siemens was useless, so I replaced it with a soldered 18650 cell, from which I immediately supply the motion sensor. A standard Siemens charger is constantly charging the battery.
First you need to solder the motion sensor with a resistor and a diode. The resistor's task is to limit the current to 10 ... 15mA so that the diode does not burn. If the 500ohm resistor works - leave it on. If the diode is too weak or the current consuming is less than 10mA - give a smaller resistor. If the motion sensor is stable, connect it permanently to the photoresistor. Both components must be protected from light. In the end, solder the photoresistor to the phone so that its shorting causes the "pressing" of the key.
Commissioning and operation.
After turning on the system, the motion sensor starts in a few seconds, the phone, fortunately, needs more time. In this way, the motion sensor will determine the operating conditions before the phone is ready to "ring". If the sensor detects motion, the "LED" will light up, which will cause a decrease in photoresistor resistance, which the phone will read as pressing the button and call the selected number.
Request. Even if you do not intend to build such a system, but you have old GSM phones at home, let us know which phones have the ability to dial with a long press.

YT movie showing action
https://youtu.be/Yl2M2v_Lsyo
Photos:
elements needed for construction
wiring diagram
Thomas
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About Author
Tomasz_72 wrote 28 posts with rating 16 . Live in city Bytom. Been with us since 2007 year.

Comments

yego666 18 Mar 2018 23:05

The idea is "ingenious" but very basic :) . If you wanted simplicity, it's definitely very simple, but I would replace the LED - Photoresistor optocoupler. It would be even simpler and then you... [Read more]

czasnagli 05 May 2018 17:32

The same and even much more can be done on the gsm Air200 -> module https://www.elektroda.pl/rtvforum/viewtopic.php?p=17200616#17200616 https://obrazki.elektroda.pl/7885478600_1525533856_thumb.jpg... [Read more]

FAQ

TL;DR: A 10-15 mA LED pulse triggers speed-dial in <5 s; "It's ingeniously simple—no microcontroller!" [Elektroda, Tomasz_72, post #17112934]

Why it matters: You can recycle any old GSM handset into a no-code motion alarm for pennies.

Quick Facts

• Supply voltage: 3.3 – 5 V DC [Elektroda, Tomasz_72, post #17112934] • LED limit resistor: 500 Ω keeps current at 10-15 mA [Elektroda, Tomasz_72, post #17112934] • PIR warm-up: Typical 5–7 s (HC-SR501 Datasheet) • 18650 Li-ion: ≈2600 mAh, 3.7 V nominal (Samsung 26J, 2020) • Air200 GSM module: US $4 on AliExpress [Elektroda, czasnagli, post #17204803]

What parts do I need for the simplest GSM motion notifier?

  1. Old GSM phone with long-press speed dial.
  2. PIR motion sensor (e.g., HC-SR501).
  3. Visible LED, 500 Ω resistor, 1N4148 diode.
  4. Photoresistor or optocoupler to mimic key press.
  5. Single 18650 Li-ion cell and charger [Elektroda, Tomasz_72, post #17112934]

How do I connect the PIR sensor to the phone’s key circuit?

  1. Wire PIR output to LED anode through 500 Ω resistor.
  2. Cathode to ground; add series 1N4148 if reverse current is possible.
  3. Enclose LED and photoresistor/opto inside heat-shrink; solder photoresistor leads across the chosen keypad switch [Elektroda, Tomasz_72, post #17112934]

What voltage and current does the setup draw?

The phone and PIR operate reliably from 3.3–5 V. Idle current ≈5 mA; alarm current peaks at 120 mA during call setup (typical GSM burst) [Siemens S55 Service Manual, 2003].

How fast does it call after motion is detected?

The PIR stabilises in about 5 s; once active it drives the LED immediately. Dialling starts within 0.5 s, so total motion-to-call latency is <5 s on a warmed sensor [Elektroda, Tomasz_72, post #17112934]

Can I replace the LED-photoresistor pair with an optocoupler?

Yes. A PC817 or LTV-817 optocoupler removes ambient-light issues and needs only 5 mA LED drive. "That would be even simpler" [Elektroda, yego666, post #17113012]

What are common failure points or false-trigger causes?

  1. Sunlight leaking onto the photoresistor can mimic a key press.
  2. A worn 18650 dropping below 3.3 V resets the phone mid-call.
  3. Long GSM bursts may brown-out if charger current <500 mA. Edge-case: In very cold rooms (<0 °C) PIR gain drops, extending warm-up to 30 s (Murata PIR App Note, 2019).

How long will one 18650 run the unit if mains fails?

A 2600 mAh cell at 5 mA idle lasts ≈520 h (≈21 days). Five 30-s calls per day add ≈60 mAh, cutting runtime to ≈38 h [Samsung 26J, 2020].

Is there a cleaner way with modern modules?

Yes. The Air200 GSM SoC costs about US $4 and supports AT commands, SMS, HTTP, and GPIO, giving richer alerts in the same footprint [Elektroda, czasnagli, post #17204803]

Could this circuit send SMS instead of calling?

Only if the handset supports SMS from a single long-press key. Most early Siemens map keys only to dial, not to messages [Siemens S55 User Guide, 2003]. A GSM module like Air200 or SIM800L is better for SMS automation.

How do I program speed dial on a Siemens S55?

  1. Menu → Phonebook → Speed Dial.
  2. Choose the key (2-9) and assign the alarm number.
  3. Exit; a long press on that key now dials automatically [Siemens S55 User Guide, 2003].

Are there legal restrictions on auto-dialing alarms?

In most EU countries, private alarms can auto-dial owners but must not call emergency numbers unless certified EN 50131 Grade 2+ (EU Alarm Standard, 2017). Always verify local regulations.
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