An emergency telephone number is a telephone number that can be used to quickly contact emergency services for assistance. Emergency services usually include police, medical, or firefighting public services. Many countries' public telephone networks have a single emergency telephone number, sometimes known as the universal emergency telephone number or the emergency services number. Most emergency service numbers are 3 digits long so that they can be dialed quickly and remembered easily. Some countries have a different emergency number for each of the different emergency services and are different only by the last digit. 