On Friday, October 12, 2018 at 9:24:31 AM UTC-4, Phil Hobbs wrote:

Providing that the thermal infrared emissivity of the surface is high,
e.g. plastic or glass. A dab of grease or some tape will make it work a
lot better.

I have not experienced that issue, for the record. What I find is that accuracy starts to suffer as the battery gets weak. I view them the same as smoke-alarm batteries - 2x per year, whether I need it or not. And the used batteries are put aside for my increasing number of novelty radios that the grandkids are fighting over. Not in them, but with them for demonstration purposes.

Peter Wieck
Melrose Park, PA