Here is a information from Honda for the alarm going off by itself. Let me know which scenario applies to you and I will try to get more information for you.
Honda Service News March 2003
Troubleshooting the Security System When It Sounds By Itself
1998-02 Accord EXs and SEs, 2001-03 Odyssey EXs, or 2003Ç03 Pilot EXs
Getting complaints from owners that the security system sounds by itself? You can determine the cause of the complaint by knowing how long the alarm sounded before it shut itself off. Here are the three possible scenarios:
Scenario 1: Alarm sounded for 30 seconds with no one in the vehicle
Scenario 2: Alarm sounded for 2 minutes while someone was in the vehicle
Scenario 3: Alarm sounded for 2 minutes with no one in the vehicle
If you can't duplicate your customer's complaint at the dealership, ask your customer to time how long the alarm sounds and to describe the conditions when it does. Having accurate info greatly increases your chances of successful troubleshooting.
Scenario 1: Alarm Sounded for 30 Seconds With No One in the Vehicle
If the security system alarm sounded for 30 seconds and then shut itself off, the Panic button on the remote transmitter got pressed and set off the panic alarm. This can easily happen if you lean over with the remote transmitter stuffed into your front pocket or you're carrying something that presses against it. This is a normal characteristic of the security system, and can't be fixed by replacing components. If your customer's vehicle is a 1998-01 Accord EX, refer to S/B 01-003, "Panic Alarm Sounds By Itself Intermittently".
Scenario 2: Alarm Sounded for 2 Minutes While Someone Was in the Vehicle
The security system alarm can sound while someone is in the vehicle. For this to happen, however, these things must have occurred in this order:
1. Someone unlocked the driver's door, opened it, and climbed into the vehicle.
2. With the door open, the person locked the doors with the power door lock switch or the driver's door lock knob, then closed the door.
3. The person waited 15 seconds or more before inserting the key into the ignition switch and turning the switch to ON (II).
The alarm sounds until you remove the key from the ignition switch and press the unlock button on the remote transmitter, or you insert the key into the door lock cylinder and turn it to the unlock position.
While the alarm is sounding and the lights are flashing, you can actually start the engine and drive the vehicle. The immobilizer system in these vehicles keeps the engine from starting unless you use a programmed ignition key, so there's no need for starter and ignition cutoff.
Because the door was locked while it was open, the security system couldn't tell if anyone was in the vehicle or just standing outside. A backup feature gives you 15 seconds to insert the key into the ignition switch to signal you're inside the vehicle. If the security system control unit doesn't detect an ignition key cylinder switch signal within 15 seconds , the system assumes that you're outside the vehicle and arms the system. This is a normal characteristic of the security system.
Scenario 3: Alarm Sounded for 2 Minutes With No One in the Vehicle
If the security system sounded for 2 minutes and then shut itself off, a security system switch was violated after the security system was armed. Here are the components that could be involved:
Door switch (any door)
Door lock knob switch (unlock)
Door key cylinder switch (lock/unlock)
Tailgate key cylinder switch (Odyssey & Pilot)
Radio security ground
Ignition switch [turned to ON (II)]
All switch circuits should be open (10 volts on the circuit) while the security system is armed. The only exceptions are the radio security ground and the driver's door lock knob LOCK inputs, which are closed (0 volt on the circuit). If any of these switches change from their normal position, (open or closed), the security system reports a violation and sounds the alarm.
The security system alarm keeps sounding until
- You disarm the system by pressing any button on the remote transmitter.
- You disarm the system by unlocking the doors with a key.
- The system automatically resets after sounding for 2 minutes
Troubleshooting for Scenario 3: Alarm Sounded for 2 Minutes With No One in the Vehicle
To troubleshoot this complaint, go to the Multiplex Control System subsection in the Body Electrical section of the appropriate S/M, and do the multiplex system self-diagnosis functions Mode 1 and Mode 2. Then do these steps:
1. Go into self-diagnosis Mode 2.
2. Lower all the windows. Close the hood, trunk,tailgate, and doors. Lock the doors.
3. Check for oversensitive hood switch, trunk switch, or key cylinder switches (door,tailgate):
- Push and pull on the hood, trunk, tailgate, and doors while listening for a beep from the multiplex system.
- If you hear the multiplex system beep, check the switch that caused the system to beep. Check the adjustment of the switch and the component that activates it. If the adjustments are OK, unplug the switch, and recheck. If the problem goes away, replace the switch.
- If the problem remains or the multiplex system didn't beep, go to step 4.
4. Check for an oversensitive door lock knob switch:
- Slowly pull up on each door lock knob, one at a time.
- If you hear the multiplex system beep when you touch the lock knob, or a lock knob is more sensitive to movement than the other lock knobs, check its linkage. If the linkage is OK, unplug the switch that's oversensitive, and recheck. If the problem goes away, replace the oversensitive switch.
- If the problem remains, go to step 5.
5. Check for an oversensitive door switch.
- Tap on and around each door switch.
- If you hear the multiplex system beep when you tap on a switch (but you don't push it), the switch is too sensitive. Look for cut or pinched wires near the area where you're tapping. If the wires are OK, unplug the switch. If the problem goes away, replace the switch.
- If the problem remains, go to step 6.
6. Check for a loose radio security ground wire:
- Remove the radio trim bezel, and then tap, wiggle, push, and pull on the radio connector and its electrical harness.
- If you hear the multiplex system beep, the radio security wire has a poor connection to ground. Tighten the loose connection. If the problem remains, check the vehicle for aftermarket accessories that sense sound or motion. If you find such an aftermarket accessory, disconnect it, and recheck.