Heat is what you get when you are not doing stuff properly. When your heat gets to about 90% guards will attack you on sight and if you are outside, you will be shot. The amount of heat you get from guards depends on the guards opinion about you. The higher a guards opinion is, the less heat you get from them, the lower the opinion, the more heat you get from guards. During a Lockdown, your heat blasts up to 99%. At 90% heat or higher, you cannot get a job. You also get heat if you are wearing a guards outfit when outside at night and day.