Where I live, it gets hot in the summer (but usually not so hot that I need AC on), but the nights usually cool down to a beautifully cool temperature. I like to open windows when it gets cooler outside in the evening, and shut them when it starts heating up in the morning. I'll usually have fans on in the windows to increase airflow, too.
However, it often happens that I don't realize it's gotten hot outside (or cooled off) until hours after the fact.
To remedy this, I'd love to find a simple two-sensor thermometer that can alert me (anything from simple beeping to smartphone notification is good) when the temperatures match or surpass each other. I'd place one sensor outside, and one inside, and it would tell me when it's time to open or close the windows. It would also be nice if it had a display with a readout of the two temperatures, obviously.
The cheaper the better; I don't have any smart home functionality otherwise, and am not looking to get into that anytime soon.
Does anyone know of such a device?