Issue wit horn and headlights

[Giliador]

When driving suddenly my horn start beeping even after engine was off it continue to beep in addition headlight went on and stay on. I removed the fuse for the horn but to stop battery from going flat I have to unplug it every time I park otherwise headlight will not go off (its a 2016 Yaris no automatic headlights) Book it in to Toyota, they told me there was no problem and everything seems to work, after 2 weeks again, car is parked horn suddenly start beeping headlight is on. Booked the car for Wednesday I'm worried again by the time I bring the car it will stop, lucky I was around the car I'm worried of this happening at night or when I'm not around the car, any suggestions what could be the cause?
Thanks

[IndestructibleYaris]

Security system activates both the horn and the lights probably, but ive never had mine trigger. Other than that, it's an electrical issue that you'll have to use wiring diagrams to trace