A security appliance is any form of server appliance that is designed to protect computer networks from unwanted traffic. Types of network security appliance:

Active devices block unwanted traffic. Examples of such devices are firewalls, anti-virus scanning devices, and content filtering devices. For instance, if you want to make sure that you do not get pointless spam and other unnecessary issues, installing an active device might be a great idea. Active devices include anti-virus scanning devices, which will automatically scan throughout the network to ensure that no virus exists within the protected network. Then, there are web filtering appliances as well as firewalls, the purpose of both of which is to ensure that only useful content and traffic flows through the network and all pointless or harmful data is filtered.

Passive devices detect and report on unwanted traffic. A common example is intrusion detection appliances, which are installed in order to determine whether the network has been compromised in any way. These devices usually work in the background at all times.

Preventative devices scan networks and identify potential security problems (such as penetration testing and vulnerability assessment appliances). These devices are usually designed to 'prevent' damage to the network by identifying problems in advance. Common examples include devices that employ penetration testing as well as those devices which carry out vulnerability assessment on networks.

Unified Threat Management (UTM) combines features together into one system, such as some firewalls, content filtering, web caching etc. UTM devices are designed to provide users with a one-stop solution to all of their network needs and internet security appliances. As the name clearly suggests, these devices provide the features of all of the other network devices and condense them into one. These devices are designed to provide a number of different network security options in one package, hence providing networks with a simple solution. Rather than installing four different devices, users can easily install one and be done with it. The market of UTM devices has exceeded the billion dollar mark already, which just goes to show how popular these devices have become amongst network users.

One of the most popular and accessible types of web security appliance tools is the hardware keylogger. This device is placed covertly between the case and keyboard with an output for the computer case and input for the keyboard. As hardware standards have changed over time, a USB hardware keylogger provides access on many devices.

The web proxy appliance is basically hardware you use to manage user web access. More to the point, it's the type of device that handles the blocking or controlling of suspicious programs. It's typically placed in between network users and the worldwide web; ergo, it's most popular application is serving as a central control hub over employee Internet use by corporations and enterprises. It's the in-between gateway that serves as a termination point of sorts for online communications within a network and is capable of applying a multitude of rule-based limitations on Internet traffic, web content, and requests before they even end up with end users.

Another commonly used hardware tool is the wireless antenna. These can be used to surveil a wide variety of wireless communications, including local cellular and internet service networks. More mechanical and general devices may include lockpicks or portable probes and hijack chips for compromising electronic devices through the physical circuit.

Secure web gateway appliances are solutions to prevent advanced threats, block unauthorized access to systems or websites, stop malware, and monitor real-time activity across websites accessed by users within the institution. Software and cloud-based platforms now perform this function as well.