# Design and Implementation of a Smart Intercom System through Web Services on Web of Things
## 1 Introduction  
As the increase in crime incidents has led to concerns about home security, it is important to have an intercom system that can help residents to understand all visitors and then allow them to enter their homes accurately [1]. The intercom systems are electronic doormen for apartments and buildings [2], but intercoms are also used to confirm that the residents are not at home before the burglars burglarize a house. On the other hand, when visitors call the intercom, the resident may be in the bathroom, kitchen, or bedroom and cannot immediately pick up the handset to answer, and the visitor will think that the resident is not at home. If the visitor is a delivery man or a postman, the resident will not receive the goods or mail immediately, which is a great inconvenience for all. The schematic diagram of the traditional intercom system is shown in Figure 1.  
Figure 1: Schematic diagram of the traditional intercom system. There has been a lot of research on improving these problems of traditional inter-coms. Door lock systems have been a hot topic in smart homes, offices, the military, and banks. Behind doors are our valuable assets, and these systems need to protect them from unauthorized people. There is a lot of research and development on security door locks based on IoT (Internet of Things) technology [3]. Users exchange information over the network using secure encryption algorithms based on IoT [4]. There is also the use of RFID and fingerprints as a dual security system [5], blockchain-based systems to establish security control mechanisms [6], and IoT-based doorbells to remotely monitor visitors in real time [7]. These articles above focuses on using various technologies to create a more secure door system, which does not solve these problems of traditional intercoms but does provide much insight. The chatbot is very useful for the practical operation of smart security systems at home and for office automation systems through the use of chatbots to alert employees when they are allowed to turn on or off the device and to notify them to turn on the fan when the temperature is high [8]. Most people use Messenger regularly to control their devices even when they are not at home, and chatbots can lock or unlock doors and check who is at the door [9]. This system deploys a chatbot server in an embedded system. It integrates a chatbot of instant messaging software to generate standardized responses through web services to build a smart intercom system on the WoT. A resident uses a menu of instant messaging software, such as \"Open Door\", \"Watch\", \"Alarm\", and \"Busy\" to communicate directly with visitors through various services and to perform the functions of door lock, camera, buzzer, and related devices, as shown in Figure 2. When a visitor presses a floor button, the resident receives a notification through the instant messaging software of the smartphone. This paper is an extension of our previous study [10]. This system adds two functions to the prototype, the camera function and alarm function, and the software framework is completely updated. This system architecture strikes a good balance between resident convenience and home security, as well as between performance and cost, effectively improving home security and reducing costs. The system allows residents to know the status of the visitors to their homes without missing any visitor messages from anywhere by using the instant messaging software on their smartphones. This paper is to integrate the chatbot server with the embedded system as the intercom host and to replace the home intercom function with the use by residents of the instant messaging software on their smartphones to realize the WoT function of the smart building. There is no need to install and learn new apps, reducing the cost of mobile phones and indoor and outdoor wiring. Whether the residents are at home or not, they can communicate with the visitors and control the status of the door through their smartphones.