They're onto me

[aleCcowaN]

I just took a glance at a "caja boba" (TV set) near the place I am and knew they're broadcasting "Liar, Liar" again. I remembered the gagreel in the credits section and a funny joke at Jim Carrey's hamming expense.

The dialog is: Lawyer: - Now let's see. "Weight: 105" ?
Fletcher Reed (Jim Carrey): - Yeah ! ln your bra.
Lawyer: - Your Honor, l object !
F.R.: - You would !
- Overactor !
- Jezebel !

[Everybody laugh]
[ Applause ]

L (pointing a finger behind the scenes)- He put me up to it.
Jim Carrey (laughing):
-"Yeah, sure he did.
Oh, no.
They're onto me."

[All Laughing]
I always doubt about the meaning of "they're onto me". Most of the time I relate it with the Argentine expression "me tienen calado" meaning "they know me well/they discovered my trick, defect or weakness", some times I think it as "la/s tienen conmigo/contra mí", and now and then I imagine it being "se la toman conmigo/contra mí".

What do you think? How can be translated all three expressions?

[Please, correct "a discreción"]

[Perikles]

I always thought it was derived from a criminal being aware of police searching for a culprit, and realising they have worked out who did it and are closing in on him/her. i.e. They have found me out.

[aleCcowaN]

Then, it would be something like "me tienen acorralado" or "me descubrieron", like "busted!" in a figurative sense.

[Perikles]

Yes, that is how I would understand it - they are onto my trail.

[laepelba]

That is definitely a phrase that would be used most "correctly" in a criminal sense, but is very commonly used for anything that is even mildly considered a secret.

I am behind in my teaching the first unit of my course, and my colleagues are onto me.
My friend's son has been hiding candy in a little-used cupboard, but his parents are onto him now.
I haven't told anyone that I was considering changing careers, but my friend Joe may be onto me because of something I said yesterday.

................

[chileno]

Then, it would be something like "me tienen acorralado" or "me descubrieron", like "busted!" in a figurative sense.

Correcto.

También "están encima mío".

[aleCcowaN]

Muchas gracias Perikles, Lou Ann y Chileno :). Ahora me quedó claro.