Switch a small DC motor from an LDR threshold using a properly rated driver, flyback protection, and hysteresis to prevent relay chatter.
Read a 24-bit pressure module only after identifying its exact sensor and protocol, then calibrate zero and span with a known reference.
Track relative methane response with MQ-4 after long preheating and calibration; use certified gas detectors for life-safety applications.
Use a reed switch as a magnet-operated contact, adding a pull-up, debounce, and suitable mechanical placement.