The key light in my 2014 Nissan Sentra iis blinking.

Seatbelt or radio code?

OK... here is YOUTUBE info on:
2005-2014 Nissan Xterra Coolant Drain and Fill 2005 2014 Nissan Xterra Coolant Drain and Fill

NICE detail, but starts with a lot of bla-bla.

Anthony

S (Nissan Vehicle Immobilizer System-NATS) has the following immobilizer functions:
Since only NVIS (NATS) ignition keys, whose ID nos. have been registered into the ECM and IMMU of NVIS (NATS), allow the engine to run, operation of a stolen vehicle without a NVIS (NATS) registered key is prevented by NVIS (NATS). That is to say, NVIS (NATS) will immobilize the engine if someone tries to start it without the registered key of NVIS (NATS).
All of the originally supplied ignition key IDs have been NVIS (NATS) registered. If requested by the vehicle owner, a maximum of five key IDs can be registered into the NVIS (NATS) components.
The security indicator lamp blinks when the ignition switch is in "OFF" or "ACC" position. Therefore, NVIS (NATS) warns outsiders that the vehicle is equipped with the system.
When NVIS (NATS) detects trouble, the security indicator lamp lights up while ignition key is in the "ON" position.
NVIS (NATS) trouble diagnoses, system initialization and additional registration for other NVIS (NATS) ignition key IDs must be carried out using CONSULT-II hardware and CONSULT-II NVIS (NATS) software. Regarding the procedures for NVIS (NATS) initialization and NVIS (NATS) ignition key ID registration, refer to CONSULT-II OPERATION MANUAL IVIS/NVIS.
When servicing a malfunction of the NVIS (indicated by lighting up of Security Indicator Lamp) or registering another NVIS ignition key ID no., it is necessary to re-register original key identification. Therefore, be sure to receive ALL KEYS from vehicle owner. System Composition NIEL0174 The immobilizer function of the NVIS (NATS) consists of the following:
NVIS (NATS) ignition key
NVIS (NATS) immobilizer control unit (IMMU) located in the ignition key cylinder
ECM
Security indicator lamp.

ANTI-THEFT SYSTEM ! Did you change KEY'S

Probably a ground. .you can check it with a test light with ignition on and off

That is a is a real good one, the airbag light has zero to do with the transmission.

I have a Nissan Sentra and the green key light inside is blinking

The blinking light doesnt mean that u have a security system it means that Nissan immobilization system (not an security alarm system) is working, which i believes comes standard on all new nissan cars now. but this feature prevents someone starting the car without a nissan key, because our keys have a microchip in it which the car can read. and if a key that doesn't have the right chip in it is used it wont turn on.

Check in your owners manual the right disarm procedure.

theres a problem with the air bag system

car is going into limp mode or you have a issue with the stock sercurity system. You will need a consult II to find out why the ses light is comming on. There is also a manual procedure but you have to count the light blinking in a pattern. its easier to go to auto zone and have them check the code.