Arduino is an open source computer hardware and software that give you the ability to make a lot of cool projects.

Can you turn on the light using the Smartphone? Yes you can with Arduino and Bluetooth module which cost less than 10$
Can you turn on the light with your voice? Yes you can with Arduino and Bluetooth module and your Android phone Yes you can
Can you send SMS to your phone when the temperature exceeds a certain limit?Yes you can with Arduino and temperature sensor which cost less than 10$

Can you make a robot car and control it using a Smartphone? with Arduino and Bluetooth module which cost less than 10$ Yes you can
Can you make a robot car that follows a line? with Arduino and line follower sensor Yes you can
Can you turn on the light/fan/alarm automatically when the temperature exceeds a certain limit? with Arduino and a temperature sensor which cost less than 10$ Yes you can

A lot of cool projects can be done with Arduino

In this course i clarify how to make these Arduino projects:

1 - Turn on and off an LED using Arduino.
2 - Read the value of temperature using the temperature sensor (LM35) and Arduino
3 - Control 220V load using Rely Kit and Arduino
4 - Turn on a 220V load like a fan when the temperature exceeds a certain limit
5 - Turn on an LED in case the object in front of line follower sensor is white
6 - Control a robot car to move in predetermined directions
7 - make a Line follower robot which is basically a robot designed to follow a 'line' or path already predetermined by the user
8 - Control an LED using Smartphone and bluetooth module and Arduino
9 - Control Robot car using Smartphone and bluetooth module and Arduino
10 -Turn on and off the light using the Smartphone
11 -Send SMS to your phone when the temperature exceeds a certain limit
12 -Turn on and off the light with your voice
13 -Control Servo motor using Arduino
14 -Measure the distance in front of the robot car using ultrasonic sensor
15 -Make obstacle avoiding robot

The Arduino project course is updated continuously so make sure to check the updates every month.

It's my pleasure answering all of your questions so please don't hesitate to ask me about anything in the course :)