Yes! Thanks for that suggestion. Same pinout on Third Reality Door Sensor. Hall effect sensor (unmarked type). Chip Output pin is open-drain with a 1M pull-up to Vdd (high=door open). Relay/other device short from Output pin (blue in picture) to Gnd pin (white wire in picture), or to actual battery ground pin/ground hole on the PCB, gives ‘low’ (door closed). I referenced DRV5023 hall effect sensor datasheet online just to confirm understanding of what I’m working with. This will soon be a power-loss sensor. With the 1M pull-up, I’m hoping an opto-isolator source fed from a USB wart via cut-up cable will be sufficient to keep Output pin pulled to near (enough) zero (low) to signal “closed” to the sensor / hub while power is enabled, and “open” (high, Out ~= Vdd) when power to USB is lost. May be some sizable time-delay from bleed-down of the USB wart, so may have to add a resistor across the opto input to make power-loss more responsive. TBD. Stretch goal: Would like to eliminate battery (replacements) for the contact sensor, so considering running sensor “battery” as a large cap charged from the USB power regulated down to ~3v. If that can run long enough, the sensor can scream “help” (door open) via Zigbee before the sensor power dies. TBD TBD.