Ponerse chango
Ponerse chango means "Be alert"
2 Answers
I recently learnt that 'chango' means monkey, when some Mexican friends came to visit.
So for those interested in the literal meaning it means 'become a monkey' because monkeys certainly are very alert.

It's the first time I hear that. I have used and is more common but informal here say:
Ponte trucha.
Ponte buzo/buza.
Pero imagino que "ponte chango" se ha de utilizar también en algunas partes.
Me voy a poner buzo caperuzo con mi inglés. haha!