Little Buddy Heater

Buddy's are designed with a thermocouple and flame jet apparatus that won't burn hot enough if the O2 starts to be depleted and the thermocouple then turns off the LP supply. It works great at regular altitudes, but at high altitude, the ambient O2 is already so low that the flame jet is reduced and won't satisfy the thermocouple.

Basically high altitude tricks it into "thinking" that it's in a regular altitude room and that the oxygen is being dangerously depleted and that it is saving your life by turning off.