I have come through Las Americas two times in the last 6 months with electroincs. The first time, I had a video projector in a carry-on bag. The second, I had a desktop in my suitcase and a laptop in a carry-on bag. Neither time was I searched nor put through the magnetometer; I was simply waved through. However, other people were directed to the magnetometer line where their luggage was being scanned. I don't know what would happen if the magnatometer detected a laptop, etc. but I assume it is nothing that a few pesos couldn't take care of.
Larry