A double stack temperature sensor housing, meant for measuring Ambient and Chamber temperature. There's a mount on the back for the ambient temperature probe and the chamber probe can be run into the small hole on the top of the P1S.

These are the temperature sensors I used:

5 Pcs Digital LCD Thermometer Temperature Monitor with External Probe for Vehicle Fish Tank Fridge Freezer Refrigerator Aquarium Brooders Climb Pet, Measure in Celsius
https://a.co/d/08S1t9US