Any device which is connected to the internet consumes bandwidth. So, the honest answer is yes, smart devices slow down your wifi. But, it depends upon the device type which you are using in your home.
Your wifi plan is another factor of how many devices it can handle at the same time. How much bandwidth are you getting in your wifi plan? What speed are you getting from your service provider?
These are the factors which you need to research about when you are going to buy smart devices to make your home smart.
Some smart devices which send video over your wifi network will definitely slow down your wifi speed.
Whereas other devices won’t affect your wifi speed. Two examples of devices which may slow down your wifi are as follows:-
Cameras:- If your home cameras are connected with your home wifi and sending video to your mobile application then it may decrease your wifi speed.
In some cases, if you receive 4k ultra hd videos then it will consume more bandwidth and slow down your wifi drastically.
Smart Doorbells:- Smart doorbells are the bells which use internet connection to stay connected with the electronic devices of the home owner such as smartphones, tablets, etc.
This type of bell will send a notification on the connected electronic device of the home when someone will arrive at the door. These types of bells may also slow down your wifi.
Now, the devices which do not consumes too much bandwidth are mentioned below:-
Smart light switches:- Smart light switches are made to control your home lights with voice assistant and mobile application. Usually, they do not consume too much bandwidth.
So, these devices won’t slow down your wifi until you use 20+ smart light switches at the same time.
Smart plugs:- Again, if you are using a few smart plugs then you won’t see any effect on your wifi speed because most of the home wifi networks are capable of handling these types of devices without any hassle.
Your home wifi speed may only get affected if you are using devices more than your wifi capability. Also, device type matters.
But, if your wifi speed is good enough and you are not using hundreds of devices in your home at the same time then you won’t see any reduction in your wifi speed.