I ordered 1 from Amazon for $18. I received a brown cardboard box with a label on it that says “Multipurpose Sensor [US]”, but inside were 2 of the purple retail-looking boxes of multi-purpose sensors. I got 2 of them.
So I think this was a mistake by Amazon where they shipped me too many. If that’s the case I’ll contact Amazon and see how they want me to ship the extra one back to them. Or they are always sent in sets of 2- I dunno.