My led remote was out of battery and I started my FX via smart start but then I couldn't unlock it with the Infiniti key for some reason?? Anyone know of why that may be?
Could you ever unlock/disarm with the OEM fob? It's likely this is an alarm programming issue. When the interface module is programmed with the Nissan/Infiniti firmware there are settings that need to be applied to allow for say use of the OEM modules.
As to alarm recommendations as others have stated Viper or Clifford would be good choices (both are manufactured by Directed Electronics). I chose the Viper 5706 which comes with the LCD remote instead of the 5906 which has the OLED screen remote. Since I have the Smart Start module as well I'll use my phone if I need/want to see details on the status of the car or for easier granular control.
Here's some things to know when you choose.
The Viper alarms have many options. If money is not a primary concern and you want the most feature rich configuration at the most cost effective price then I'd chose the following:
5706v (second to top alarm but with black and white instead color LCD remote so saves you 100 bucks).
Option: Smart Start module (if you want cell phone integration and app based control. With service you can control/monitor your car from anywhere.
DBALL2 interface: This interface module allows the alarm to talk directly to the cars computer via the OBDII port. You will require this to use your alarm effectively in the FX.
T-Harness: This is optional but if you spring for this harness it will allow installation of the alarm into the vehicles systems with virtually no wire splicing/cutting at all. It has plugs that plug into the existing factory harnesses.
Option: Bluetooth module. This will allow you to use your phone to control the alarm but ONLY from within bluetooth range. I don't find this worthwhile since once you are actually at your car the only thing you'll really want to do is unlock and enter. Since the bluetooth range is 30ish feet it's useless from far away.
Also note that there are tricks you can do with the alarms and appropriate programming. Such as using the AUX lines (there are 4 on the 5706 for example) to signal other things (like send power to a relay to turn a computer on before entering the car).
I bought all of the options above except for the Bluetooth interface.