You can try an interior doorknob which is unique like some glass doorknobs. E.g. one can get say the quality of Tascam GVI with 7GigaBytes (7000 MegaBytes) of quality sounds for £199 ! https://xn--L3Ca4b8epb5b.com/category/%E0%B8%84%E0%B8%A5%E0%B8%B4%E0%B8%9B%E0%B8%AB%E0%B8%A5%E0%B8%B8%E0%B8%94%E0%B8%A1%E0%B8%B2%E0%B9%83%E0%B8%AB%E0%B8%A1%E0%B9%88/