[23 - infrared / flame detection]
[48 - actuators]
[20 - heartrate]
And maybe also combined with the peripheral oxygen saturation SpO2. Hosipitals use these sensors to see if there is enough oxygen in your blood during the operation. This sensor also measures your heartrate. Maxim makes this sensor for instance (MAX30102). http://media.digikey.com/pdf/Data%20Sheets/Maxim%20PDFs/MAXREFDES117_Web.pdf
[15 - liquid tank levels ]
[49 - magnetic switch]
[ 48 - actuators]
If only the top-hat of the probe was waterthight
yes it needs some DIY .. ..
[ 41 - inductive proximity ]
Soil Temperature/Moisture Sensor Probe (SHT10)
[6 - movement DOPPLER]
The RCWL-0516 is 0.99$ and up. Not tested yet.
one BIG difference between PIR and DOPPLER/RADAR.
radar sensors also detect through a door or a wall and are very sensitive.
they consume more or less the same.
38 - radiation