Two thousand feet of half-inch PEX already slept six to eight feet under Craftsman Chris’s yard when his first homemade cooling plan came up short. Four parallel five-hundred-foot slinky loops and a Taco 009 pump pushed water through a heat exchanger in the furnace plenum, yet the dirt had baked in the sun after excavation and the loop stayed warmer than he needed. Direct ground water barely cooled the house. He needed a machine that could pull heat out of indoor air and dump it into that soil instead of into hot summer wind.

Dr Semiconductor already had working DRAM cells from a class 100 cleanroom built inside a home backyard shed. Packaging those silicon chips onto a circuit board was the next problem, because silicon is opaque and lining up pads by eye is a guessing game. Gallium nitride grown on sapphire is transparent, already contains the layers that make blue light, and happens to be the same material used in commercial LEDs. A two-inch epiwafer costs about $160 and lasts a long time once you dice it.

Comcast started rolling out Xfinity Shield this month, and the free piece that has everyone talking is WiFi Motion. Eligible internet customers who rent a recent Xfinity gateway can turn their existing Wi-Fi into a basic movement watcher without buying cameras or extra sensors. Radio waves already fly between the gateway and other gadgets that stay plugged in. A person walking through those paths changes how the waves arrive, and software in the box treats that change as motion.