Bypass the alarm
If you have the key you should be fine. Check your owner's manual for how to shut the alarm off once you're in the car with the key in the ignition if it does't shut itself off. Again, once you're in and have it running you can simply pull the relay under the hood to make the horn and lights stop. You will also have no horn though, and the security system will still be functioning, it just won't be making a bunch of noise. If it actually won't start with the key, or if you don't have the key or if it is perhaps not your vehicle you will need to have it towed to a dealership for them to sort out.
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