What does a security gateway do?
A gateway sits between the devices at a site and the cloud service that manages them. Its first job is discovery: using ONVIF, a common open standard, it scans the local network and finds compatible cameras, asks each one what streams and features it offers, and presents them to the platform without someone typing in addresses. The installer plugs cameras into the same network, and the gateway does the introductions.
Its second job is the uplink. Instead of every camera needing its own route to the internet, the gateway collects their video and status and sends them out over one managed connection, usually outbound and encrypted. That centralizes security and makes cellular sites simpler, since only one device negotiates with the carrier network. Its third job is acting as a bridge to the physical world through its input and output connections.
How do digital inputs and outputs work?
A digital input is a pair of terminals that can tell whether a circuit is open or closed. A door contact, for example, closes a loop when the door is shut and opens it when the door moves. The gateway watches that loop and reports a change as an event. Inputs can also read other simple switches such as a push button, a tamper switch inside an enclosure, or a dry contact from an alarm panel.
A digital output works in the opposite direction: the gateway changes the state of a terminal on command. The output is a signal, not a power source, and it can handle only a very small load. It might drive the coil of a relay, or tell a siren controller to start. Because inputs and outputs are binary, simple and predictable, they remain a dependable way to link equipment from different makers, even in an era of complex software.
What is a relay and why use one?
A relay is an electrically operated switch. A small current through its coil creates a magnetic field that moves a mechanical contact, and that contact opens or closes a separate circuit that can carry far more current or a different voltage. This isolation is the point: the delicate electronics of the gateway control the circuit but never carry its load, so a strobe, a floodlight or a siren can be switched safely from a low-power signal.
Choosing a relay means matching it to the load. Look at the voltage and current the load needs, whether it runs on direct or alternating current, and whether the load is inductive, like a motor or horn, which creates voltage spikes when switched off. Normally open contacts close only when activated, while normally closed contacts do the reverse. Wiring and fusing should follow local electrical rules, and a qualified installer should confirm the design.
What are RS-232 and RS-485 serial ports used for?
Serial ports are an older but still common way for devices to talk. RS-232 connects two devices over a short cable and is typical for configuration ports and some alarm panels. RS-485 is built for longer runs and can link several devices on one shared pair of wires, which is why it appears in access control readers, environmental sensors and industrial equipment. Both send data as a stream of bits, following a protocol agreed by the two ends.
A gateway with serial ports can therefore read from or command equipment that has no network connection at all. A sensor that reports a value over RS-485 can be polled by the gateway and forwarded to the cloud as an event. The practical catch is configuration: both ends must agree on speed, data format and addressing, and the protocol is defined by the equipment maker. Ask for documentation before assuming two devices will cooperate.
How do IoT sensors and webhooks fit in?
IoT sensors extend what a security system can notice beyond video. Door and window contacts, motion detectors, water leak sensors, temperature probes, vibration or tamper switches and gate position sensors all produce simple events. Wired ones connect to inputs, while wireless ones talk to a receiver that is itself connected to the gateway. Each event can be given a name and a location, so an operator sees 'rear gate open' rather than a cryptic input number.
Webhooks provide the software equivalent. A webhook is a message sent over the internet to a web address when something happens, carrying details such as time, source and type. A platform can receive webhooks from other systems, such as access control or point of sale devices, and can also send them to trigger outputs elsewhere. AI VisionStream supports API and webhook integration, which lets video events and outside data feed the same automation.
Can a gateway run analytics, and how do you choose one?
Some gateways include a neural processing unit, a chip designed to run AI models efficiently. That lets analytics such as object detection run on site rather than in the cloud. The benefits are lower bandwidth, since only events and short clips need to travel, and faster reaction, since the decision happens beside the camera. The trade-off is that the chip's capacity is fixed, so it can run a limited number of streams and models.
When choosing a gateway, count what you need to connect: cameras, inputs, outputs and serial devices, with some spare. Check whether outputs are dry contacts or driven signals and what load they can handle. Look at the operating temperature range and enclosure rating if it lives outdoors, the power input it accepts, and what happens during a network outage. A good gateway keeps local logic and local recording working and reports back when the link returns.
Key terms
- Gateway
- A small on-site device that discovers local cameras and sensors and connects them to a cloud platform over a single managed link.
- Digital input
- A terminal pair that detects whether an external circuit is open or closed, used for door contacts, tamper switches and similar signals.
- Digital output
- A terminal the gateway switches on command to send a low-power signal, typically to a relay, siren controller or similar device.
- Relay
- An electrically operated switch that lets a small control signal open or close a separate circuit carrying a larger load.
- RS-485
- A serial standard for longer cable runs that lets several devices share one pair of wires, common in sensors and access control.
- Webhook
- An automatic message sent to a web address when an event occurs, used to pass information between software systems or trigger actions.
- Dry contact
- A switch contact that supplies no voltage of its own, simply opening or closing a circuit that another device powers.
A trailer like this carries cameras that support ONVIF and RTSP, a dual-SIM 4G/5G router and native DC power distribution at 12, 24 and 48 volts, which suits low-power sensor and relay wiring. IP speakers and strobe lights are available for live talk-down and deterrence, and AI VisionStream rule-based automation workflows can drive talk-down speakers, lights or relays and escalate to an operator when a camera detects an intruder.
Common questions
What is the difference between a relay and a digital output?
A digital output is a low-power signal from the gateway that can only drive a very small load. A relay is a separate switch that the signal operates, letting a small current control a larger circuit such as a strobe, siren or light. The two are often used together.
Can a gateway work with cameras from different makers?
Generally yes, if the cameras support ONVIF, an open standard that lets a gateway discover them and read their streams. Support varies in depth, so confirm that the features you need, not just basic video, work through the standard before you buy.
Do I need RS-485 or serial ports for a typical site?
Often not. Many sites need only cameras and a few inputs and outputs. Serial ports matter when you must connect equipment with no network interface, such as certain sensors, access readers or alarm panels. List your devices first, then check their interfaces against the gateway.