You don't need smart switches. Keep the ones that match your sockets.

Here is something the smart-home trade seldom volunteers: the switch on your wall does not need to be smart. In a KNX villa the intelligence lives in the distribution board, and all the switch has to do is tell the board that somebody pressed it, which any decent push switch can manage. This article explains how that works, why it matters for your walls and your bill, and when a keypad is genuinely worth having.

What happens behind the wall

A KNX villa keeps its actuators in the distribution board: relay channels that switch circuits and dimmer channels that dim them. They listen on the bus and act when a message arrives, and that message can come from anything able to send one, be it a keypad, a screen, a sensor, a phone, or a small device called a binary input.

A binary input sits flush in the back box behind an ordinary switch and has a few contact inputs of its own. When you press the switch, the contact closes, the binary input sends its message, and the actuator does whatever the design asked of it, which might be a single circuit, a whole scene, or dimming on a long press. The switch itself stays simple and inexpensive, and it is yours.

Why it matters more than it sounds

Your switches match your sockets. Every villa has a socket series chosen for its interior. In many smart-home designs the keypads come from the automation brand instead, and they look as though they were fitted in a different building. With binary inputs, the switches come from the same series as the sockets, in the same finish, and the wall reads as a single piece of design. That is one of our own rules: one visual language on the walls, meaning one brand, one series and one finish.

It costs nothing on our bill. The switch line reads AED 0 because we do not sell switches, and the binary input appears as a small line of its own. You buy the switches wherever you buy the sockets, from any brand, at whatever price your fit-out company gets them.

It removes the keypad tax. Branded keypads are priced as automation hardware, and once they are multiplied across every room, a good part of what people think of as the cost of automation turns out to be the cost of the buttons. Take the buttons away from the automation brand and the number falls, with nothing working any worse.

It can be replaced in an afternoon. When a switch breaks, the client buys the same one from the same shop and the electrician swaps it over. There is no automation brand to go back to, no lead time and no programming.

When a keypad earns its place

A keypad earns its place when a room needs several scenes at one point and a plain switch would need too many gangs to carry them. That is a real case, and when it is real we design for it. What we do not do is put a keypad in every room by default. The rule we design to is one primary control point per room, at the door, with buttons that are scenes rather than one button per circuit, so a kitchen with seven circuits gets about four scene buttons, not sixteen. If a plain two-gang switch can carry those scenes, it does.

Keypads therefore appear on our bills as an option, chosen room by room and priced as what they are. Screens are a different matter. A room screen is the thermostat, and a conditioned room needs one way to set its temperature, so where a room needs climate control it gets a single climate surface. That is usually a screen, though on some brands a display keypad does the job, and it carries the room's scenes as well.

Two things the site must get right

The switch must be retractive. That means a push switch that springs back, not a rocker that stays down. A rocker stops matching the light the moment a scene or the app changes something, and from then on nobody trusts the wall. Most socket series offer a retractive version, and the documents we give your electrician say so plainly, so it is worth checking before the plates go on.

Wire it as the design says. The binary input needs both the switch wires and the bus pair brought to the same back box. The first-fix schedule in the contractor documents shows the box, the height, the conduit and the cable for every point, and a site that follows it has switches that work on the first day.

Why every bill carries an AED 0 line

Every Homestat bill carries the AED 0 line. It is there so you can see that the switches were not forgotten: they were designed out of the bill on purpose. If someone quotes you a keypad in every room, ask them why the maid's room needs one, and then ask what a binary input costs. If they cannot tell you, that is an answer in itself.

See what a bill looks like or send us your plans.