Door Release Transformer; Where Is It?

I own a 1960 atrium model Eichler in Sunnyvale. The electric door release stopped working, and my electrician has determined that the transformer needs to be replaced, but is unable to find it. It is not in the boiler room where the doorbell one is, and he suspects that it is in the garage on the wall that is adjacent to the atrium. The problem here is that a prior owner drywalled that wall clearly covered it when doing so. My electrician wants to take an educated guess and break through drywall to find it, but I thought I would also ask here. ~1960 Eichler owners, where are your transformers for your door release button?

Thanks!