Multiple iPhone Duo reviews covered the device's thermal properties, and reviewer opinions varied. Some found that it was just warm, while others thought it was running too hot at times. Joanna Stern said the back of the device got warm when using FaceTime and taking photos. She had to end a FaceTime call during testing because it got too hot. "Yeah, I'm gonna burn my hand off," she said. "This thing is getting really warm".

Multiple iPhone Duo reviews covered the device's thermal properties, and reviewer opinions varied. Some found that it was just warm, while others thought it was running too hot at times. Joanna Stern said the back of the device got warm when using FaceTime and taking photos. She had to end a FaceTime call during testing because it got too hot. "Yeah, I'm gonna burn my hand off," she said. "This thing is getting really warm".