At Amazon, get this Airthereal Touchscreen Radon Detector for $60. It's the best deal Amazon has offered for this model.
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Features Measures radon levels starting at 0.09 pCi/L 3.4" color touchscreen display Trend graphs covering 6 to 96 hours Audible and visual alarm w/ custom radon threshold Rechargeable battery w/ USB-C charging One-touch PDF report export