Electronically monitoring whether or not your car block heater is connected to a mains outlet might at first seem like an arbitrary task. A device installed in the comfort of the car seating area, which tells the user at every startup whether or not his/her car is connected to a mains outlet, could have market appeal though. But in order for it to be a worthwhile idea to pursuit, a certain requirement has to be met. It has to be able to be able to accurately detect whether or not the car is connected, through a single connection; the car ground. A certain part of the voltage in the phase of the mains will be capacitively coupled upon the safety ground. By exploiting the fact that the car ground will be connected to the mains safety ground when the block heater cable is in use, a device which can detect that coupled voltage could possibly be developed. In other words, a cable monitoring unit which in actuality detects a connection to the mains safety ground through capacitive coupling, hence the title of this dissertation. This work sets out to taking appropriate measurements to find out whether or not this proposed method of safety ground detection is valid, with heavy emphasis on whether or not it is applicable to a cable monitoring unit. According to the measurement results, an appropriate device is developed. A device which can fill the function described in the previous paragraph. Development of such a device involves; proper method of supplying power which upholds a galvanically isolated floating ground, signal processing, reliable detection mechanism, and considerations to how unintentional capacitive coupling behaves. A theoretical model of the device is put forth, as well as an actual rough prototype to in practice try to prove that the concept and method is valid. Downsides and problems with the device are discussed, such as upholding an effective detection system without making the device hard and cumbersome to use. Possible solutions to these problems are also proposed. The possible future of the concept of this device is also touched upon.