If a toyota highlander alarm goes off randomly, what is the problem?

The number one reason for the alarm going off randomly in a Toyota Highlander will a faulty hood latch switch. The metal connectors will corrode over time and cause spikes in resistance causing the alarm to go off. The switch is located inside the hood latch assembly. To replace it, remove the three 10mm bolts holding the latch in, the center one has a plastic cap the needs to be pried off. Pull the latch up and disconnect the hood release cable and switch electrical connector. Replacing the entire hood latch assembly will cost around $50 using aftermarket parts, which is cheaper than trying to just replace the sensor, which can cost up to $80. To keep the alarm from going off, You could just remove the electrical connector until You can replace the latch, but the alarm will not set.