There are two ways to check if someone is stealing your electricity. Order an inspection of your electrical system from an electrical company. They will charge a fee for this service. However, it is not possible to prove any theft if the neighbour is not stealing your electricity at the time of the inspection. Another option is to check your consumption at different times. Switch off all electrical appliances, including the fridge, and monitor your electricity meter for a while. If the indicator light of the electronic meter keeps blinking, your suspicions might be correct.