Pipe Freeze PRO heat tape is designed with a built in thermostat to reduce power consumption (to effectively nothing) when temperatures are high enough that pipes won’t freeze. It is because of this function, that when you plug in your Pipe Freeze Pro Heat Tape, you may not feel any heat.
You can test your Pipe Freeze Pro Heat Tape by resting an ice pack (a ziplock bag filled with ice will suffice) on the thermostat and plugging in your cable. Once this is done, the cable will be slightly warm to the touch within 30 minutes.
Keep in mind that the self-regulating cable gets warmer as the temperatures it is in contact with are colder, so unless you are in an area where the ambient temps are below freezing the temperature of the cable will remain relatively low.