run an LED (node ?) dimly on a few microamps, and you can run it for years off of a button cell.
by @JoachimHummel
biomedical monitor with MAX32620FTHR
Chiiiiiirp! Indoor Air Quality Measurement and Alarm
Perhaps also nice to know, if you take a magnetometer with you in your car you can see in the data when you cross a bridge on a highway. Perhaps due to bias voltages on the metal to prevent corrosion, or because metal objects pass over it over and over in the same direction (like magnetizing your screwdriver with a magnet). Some bridges distort the magnetic field more then others. Found this out while driving on the A12 near Utrecht, The Netherlands.
Hi, yes interesting, and that’s the biggest hurdle in designing a carpark detector, it must detect cars in only one parking space, and not the ones left and right from it, also when a big metal object, like a truck, passes they must not react.
Semi-robust GPA for my single channel GW on my caravan, will get some epoxy to. Still the only one with a node here, the rest must be on a different SF or channel… 
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I also use the principle of distorted (earth-)magnetic field to catch shoplifters in the shop where my wife works. Some people use magnets to take off security tags. It already has detected insulated shopping bags, and some obscure people that they then gave extra attention. It also performs good as a detector for wheelchairs and rollators. A simple, but effective sensor. My goal now is to make it energy efficient, so that you can place it anywhere, and let it use LoRaWAN, so that I can monitor and tweak it.
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about the design of the board : http://www.rocketscream.com/blog/2018/06/18/single-cell-arduino-compatible-lorawan-low-power-node/
Arduino Data Glasses for Multimeter
waiting for the first paxcounter glasses 