Batboard

I was in the MCX 1000 yesterday and found a "proper code detect" option in the MCX 1000s. Will this allow me to listen to someone using a different code?

Not at all.

Proper code detect is a PL/DPL decoding action for radios using PL on both transmit and receive, and what proper code detect does, is keep the receiver 'muted' unless the correct PL tone is decoded by the radio, then the receiver wil 'unmute' and you will hear the conversation/call.

This also is used when operating secure radios, as the receiver will remain muted unless the proper encryption code is decoded by the encryption module.

A codeplug is the radio's operating frequencies, tuning and alignment and has nothing to do with transmission or reception.