Mistake in Example

In the introduction video of Internet of things
Example was given that temperature should be between -30 to -40
But it triggers a alarm at -31°
It should be -29° as negative values have more value when they are near to zero.

The temperature must lie between the extreme points i.e -30 and -40. So as the temperature reaches -31, a slight increase in the temperature and it will cross the extreme point -30. Hence at -31 an alarm is triggered to warn the change in temperature.

Can you tell me the acceptable points between 30°-40°

I can understand you watched the video but it was a small mistake made at the time of video making.

And they might not noticed it in a hurry

In the video they clearly mentioned the threshold temperatures to be -40 and -30. They also mentioned that the temperature had reached -31 and it was rising. If it crossed -30 the environment conditions would become unfavorable for production. Hence at -31 an alarm was set to warn them to check any defects before it crosses -30. So alarm had to trigger before the threshold temp. i.e -31. The acceptable points are [-40, -30] inclusive. I hope it clears your doubt.

They said temperature is set between -30° to -40°
So the acceptable temperature include -31°,-32° and so on
By mistake they said -31° instead of -29°

Get your math right
Because -1 is greater than -100

Just think about this. If the temperature is -35 and it is increasing then which one will come first, -31 or -29??
-31 right??? Now you are saying alarm should trigger at -29 but you are wrong here. If alarm were to trigger at -29 then it would be of no use because temp. already crossed the threshold -30. Hence alarm is triggered at -31 so that before crossing -30 people can be warned and can have some time to act before temp. crossed threshold.
You are getting confused in negative increasing numbers. Draw -41 to -29 on a number line. You will get the point.