A remote starter is a radio control

Radio control

Radio control is the use of radio signals to remotely control a device. The term is used frequently to refer to the control of model vehicles from a hand-held radio transmitter...

led device, which is installed in a vehicle by the factory or an aftermarket installer to preheat or cool the vehicle before the owner gets into it. Once activated, by pushing a button on your keychain remote, it starts the vehicle automatically for a predetermined time. Different models have keyless entry

Remote keyless system

A remote keyless system is a system designed to permit or deny access to premises or automobiles. While the "remote" system is portable and has locking capabilities, the exact phrase "keyless entry" is solely reserved for the numeric dials or keypads that are located on or near the driver side door...

 as well. Most newer vehicles need some kind of bypass module to bypass the factory anti-theft system

Anti-theft system

An anti-theft system is any device or method used to prevent or deter the unauthorized appropriation of items considered valuable. Theft is one of the most common and oldest criminal behaviours...

, so the vehicle can be started without the ignition key

Key (lock)

A key is an instrument that is used to operate a lock. A typical key consists of two parts: the blade, which slides into the keyway of the lock and distinguishes between different keys, and the bow, which is left protruding so that torque can be applied by the user. The blade is usually intended to...

in the ignition, this is bypassed only to start the vehicle, which after it is running returns to its original state. Having a remote starter installed in your vehicle will not void your factory warranty when installed properly.