The Power Detect (PWR DET) is used to monitor the state of the internal charge pump regulator. The block only has one output (OUT) but a few configuration settings must be set in order for the pin to be enabled.
In order to use the PWR DET output, the project settings must be correctly configured. In the general project settings (Project Settings button -> General tab) Power supply control mode must be set to Charge pump automatic ON/OFF and Disable power auto detector function for charge pump set to Enabled.
Once the settings have been properly configured, the PWR DET output is HIGH when VDD<2.7V and LOW when VDD>2.7V.