Introduction
With the US Hot Cars Act requiring child presence detection in all new passenger vehicles by the 2028 model year, automotive-grade PIR sensors are becoming a critical component. This article covers the technical requirements and implementation considerations.
Regulatory Context
The Hot Cars Act (HR 3164) mandates:
- Detection of a child left in the rear seat after ignition off
- Alert within 60 seconds of vehicle shutdown
- Audible and visual alerts distinct from other vehicle warnings
- System must be operational for at least 3 hours after shutdown
- Self-diagnostic capability with fault indication
Automotive-Grade Requirements
AEC-Q100/200 Qualification
Automotive sensors must meet AEC-Q100 (for ICs) or AEC-Q200 (for passive components) standards. This ensures reliability under automotive operating conditions.
Temperature Range
Vehicle interiors can range from -40°C to +85°C (or higher in direct sun). Automotive PIR sensors must operate across this range without performance degradation.
Sunlight Rejection
Direct sunlight through windows can saturate PIR sensors. Automotive-grade sensors have enhanced optical filters and temperature compensation to handle sunload conditions.
Vibration and Shock Resistance
Vehicle operation exposes sensors to continuous vibration and occasional shock (road impacts, door closing).
EMI/EMC Compliance
Sensors must withstand electromagnetic interference from vehicle electrical systems (ignition, motors, radios) without false triggers.
Sensor Placement
Automotive child presence detection typically uses 2-3 sensors placed in the headliner above rear seats. Sensors should be angled to cover the entire seat area, including child seats. Some designs use sensors integrated into the rearview mirror or B-pillars.
Detection Algorithms
Modern systems use machine learning algorithms to:
- Distinguish children from other objects (bags, groceries)
- Detect stationary children via micro-movements (breathing)
- Ignore false triggers from sunlight and temperature changes
- Integrate with door lock and ignition status
Automotive-Grade PIR Sensors
Panasonic EKMB Automotive Series (AEC-Q100)
Voltage: 2.3-4.0V
Current: 1-6µA standby
Temperature range: -40°C to +85°C
Features: AEC-Q100 qualified, available with various lens patterns, excellent temperature compensation
Excelitas DigiPyro Automotive Series
Voltage: 2.7-5.5V
Current: 2-5µA standby
Temperature range: -40°C to +85°C
Features: AEC-Q100 qualified, digital output, integrated wake-up mode
Integration with Vehicle Systems
Alert Systems
When a child is detected after vehicle shutdown, the system must trigger:
- Audible alerts (horn, chime)
- Visual alerts (dashboard warning, lights)
- Mobile app notifications (via telematics)
- Emergency services contact (in some designs)
Power Management
Sensors must operate with vehicle power off (battery mode) for up to 3 hours after shutdown. Ultra-low power consumption (1-10µA) is critical to avoid draining the vehicle battery.
Conclusion
Automotive child presence detection represents a major new application for PIR sensors. With the 2028 mandate approaching, qualified automotive-grade sensors from Panasonic, Excelitas, and Murata are becoming essential components for vehicle manufacturers.