At one parish near me, the door to the confessional from top to bottom apart from the frame - which is metal - is clear glass. As you enter, there is a kneeler with a opague curtain for a screen slightly to the left, and Father sits behind this screen. There is also a chair straight ahead, which places you directly opposite Father for a face-to-face confession. I believe this is a good way, as the penitent sitting in the chair is in full view (consider clergy sex abuse), so anyone glancing in would see any funny business if it were to occur. Any sounds are extremely muffled, so on odd occasions it is possible to hear muffled voices - though no words.
At my own parish, we have the traditional confession. Father sits on one side in his ‘own room’ and enters through his door. The penitent enters through their own separate door, and kneel down behind the grill which also has a thick curtain on Fathers side. This way, the penitent can be heard but not seen, and there is no opportunity for anything to occur as both are in ‘separate’ rooms.
I have also gone to confession at a parish where the priest hear confession in the sacristy and had his back to the door, (not safe for his really, after all, somene could come up and whack him over the head and rob the sacristy), with a kneeler placed behind his shoulder.
Also I’ve been to confession, where due to the large numbers of penitents waiting in line for confession, another priest sat up front in the first pew and people knelt in the pew behind him, or sat next to him, whichever they preferred.
As people usually arrive when there is at least one other person waiting, or if the first there, are waiting for Father to arrive, then they are seen and it is obvious they are waiting for confession - so why would it matter if someone ‘saw’ you making your confession?