Custom 3-PIR GSM Anti-Theft Security Alarm with SMS, Call & Relay

Custom 3-PIR GSM Anti-Theft Security Alarm with SMS, Call & Relay PROJECT DESCRIPTION: I am looking for an experienced embedded hardware and firmware developer to design and develop a custom human motion / anti-theft security alarm using an ATmega328P (Arduino-compatible) microcontroller. The device will use 3 external PIR motion sensors connected to the main PCB through long cables. The main feature is a selectable PIR detection threshold of 1, 2, or 3 sensors. This will help reduce false alarms. MAIN PIR LOGIC: The device has: * PIR 1 * PIR 2 * PIR 3 The user can select the required number of PIR sensors that must detect movement. Threshold 1: Any one PIR becomes active = intrusion confirmed. Threshold 2: Any two PIRs become active = intrusion confirmed. PIR1+PIR2, PIR1+PIR3, PIR2+PIR3 or all 3 should trigger. Only one PIR should NOT trigger. Threshold 3: All 3 PIRs must become active = intrusion confirmed. The threshold should preferably be selected using a physical 1/2/3 selector, such as a rotary switch or suitable DIP/selector switch. When an intrusion is confirmed: 1. Trigger relay output 2. Send SMS 3. Make phone call 4. Show status through LEDs PIR SENSOR CONNECTION: All 3 PIR sensors will be external and connected to the main PCB through separate connectors. The PIRs will use long cables because they may be installed at different locations. The PCB/firmware should consider: * Long cable operation * Electrical noise * Signal interference * Proper grounding * Input protection/filtering * Reliable HIGH/LOW detection * Suitable connectors Please recommend the suitable connector and practical maximum cable length. GSM: The device must support: * SMS * Voice calling * SIM card * Approximately 4–5 emergency phone numbers Please recommend the best currently available GSM/cellular module for this project based on: * SMS reliability * Voice call support * Network availability * Power consumption * Current peaks * Long-term product suitability * Availability and cost * Bangladesh network compatibility Do not automatically assume SIM800L is the best option. Please recommend the appropriate module for a new commercial product. The GSM power supply must be properly designed because GSM modules can have high current peaks during transmission and calls. SMS: When an intrusion is confirmed, send an alert SMS to the configured phone numbers. Example: "ALERT! Motion detected. Please check the location." Approximately 4–5 phone numbers should be supported. Phone numbers must be stored in non-volatile memory (EEPROM or equivalent) and remain saved after power loss. Please recommend the easiest customer configuration method, such as SMS commands, PC configuration, or another practical method. PHONE CALL: After a confirmed intrusion, the device should automatically call the configured emergency numbers. Please implement sensible call logic with timeout/retry control so the device does not continuously call all numbers. The exact call sequence can be finalized during development. SMS/CALL ON/OFF: There will be a dedicated physical SMS/Call ON/OFF switch/button. When OFF: * PIR detection continues * Relay can continue working * No SMS is sent * No phone call is made When ON: * SMS and calls operate normally RELAY: One relay output is required for an external device such as: * Siren * Alarm * Light * Other security equipment Use proper relay driver and protection circuitry. STATUS LEDs: Provide clear status LEDs for: * PIR detection/status * GSM/network/SMS/call status * Alert/communication status Exact LED behavior can be finalized with the developer. MICROCONTROLLER: Preferred MCU: Microchip/Atmel ATmega328P. I prefer the ATmega328P to be directly integrated into the custom PCB rather than using a complete Arduino Uno board. Firmware should be Arduino-compatible C/C++ and fully provided with source code. BATTERY: Power source: 3 × 18650 rechargeable Li-ion batteries. The battery holders will be mounted directly on the main PCB. The PCB must include: * Battery connection/holders * Battery charging circuit * Battery protection * Buck converter/regulator * Proper power distribution Please recommend the best battery configuration and power architecture. CHARGING: Integrated charging circuit with external charging port. The design should include appropriate: * Li-ion charging * Overcharge protection * Over-discharge protection * Short-circuit protection where appropriate * Charging indication if practical POWER MANAGEMENT: Proper regulators/buck converters must be selected for the ATmega328P, PIR sensors, GSM module and relay. The GSM supply is especially important. The circuit must handle GSM transmission/call current peaks without causing voltage drops, GSM resets or ATmega resets. Use appropriate bulk and decoupling capacitors and proper PCB power/ground design. POWER SWITCH: Include a physical main ON/OFF switch for the device. SIM: Include a suitable SIM card holder that is reasonably accessible. PROGRAMMING: Provide a programming/debug connector so the ATmega328P firmware can be updated without removing the MCU. Please provide programming and firmware update instructions. FIRMWARE: Firmware should include: * 3 PIR monitoring * 1/2/3 threshold selection * PIR confirmation/timing * Relay control * SMS * Phone calling * 4–5 phone number storage * EEPROM storage * GSM timeout/recovery * Network reconnect where possible * Watchdog timer * Protection against repeated SMS/calls * Safe startup/restart behavior The system should avoid sending repeated alerts continuously from one long PIR activation. A suitable cooldown/alarm state should be implemented. PCB DESIGN: Create a complete custom PCB containing: * ATmega328P * GSM module * SIM holder * 3 PIR connectors * Relay and driver * Status LEDs * 3 × 18650 battery holders * Charging circuit * Buck/regulator * Main ON/OFF switch * SMS/Call ON/OFF switch * 1/2/3 PIR threshold selector * Charging connector * Programming connector * Required protection component