How to disable 98 Toyota Avalon Alarm

If I remember correctly if you unlock the drivers door with the key from outside twice it disables the arm just like the key fob would have but only if it is a factory alarm system.

If the alarm system has a battery remove it otherwise removing the car battery for a while may reset it. In emergency contact your local toyota dealers mechanics department and they may be able to help you at no cost.
If you put a general enquiry on google you might get lucky, do not be too specific. i.e. toyota 1994 alarm reset procedure

Have you locked and unlocked the driver door with the key ?

sounds like a weak battery make sure u are getting 12 volts or better from the alternator

When you close the door, the alarm will arm itself even if you do not set it. When you open the unlocked door, the alarm will sound.

no problem, connect battery and then use key to lock and then unlock the driver door, this will shut down alarm. hope this helps.

Same here... I have a 1998 Toyota Avalon XL. My car battery died. Replaced my car battery, but found out that when you unplug and plug the car battery with this car it engages in security mode (I have factory car alarm). This disables the engine and wont let you turn the ignition aka start the car engine until the remote (keyless entry) "UNLOCK" is applied. My remote is also lost so I cannot disable the alarm.
The only thing I can think of to do is unplug the battery again to disable everything (car alarms are annoying...) and call the dealer to pick the car up and perform the diagnosis. Most likely they will offer you another keyless (ugh... expensive) and/or you could ask to disable the factory car alarm.
I know thats not much help but it seems to be the only option from what I researched currently....

when you disarm the alarm make sure you hear a beep beep sound twice before you try to start the car.

Without the schematics for the alarm. I would look for the alarms controller /relay and remove it. Use fuse diagram in the owners manual to see whats stock and whats not if its an aftermarket alarm.

Check the fuses, relays, anti theft and security system.