How can I connect multiple applications on an Arduino?

Basically, I want to control multiple application using a smartphone to an Arduino.
If I want to control lightbulb, security camera, garage door, and security sensor, can I use only 1 Arduino or I need 4 Arduinos to connect to 4 applications?
Is there a specific Arduino board should I use? Do you recommend of using an Arduino BT since I am connecting it to a smartphone?

orksecurity6 years ago
As Steve says, the problem is underspecified. The responses to the other copy of your question provide some information about what it takes to have one microcontroller monitor multiple inputs and control multiple outputs.

You also need to define what "connecting to a smartphone" means. How are you planning to make the connection? (Both hardware and software details matter.)
Define what YOU mean by "control" here.