Sound detectors without electronics largely boil down to mechanical enhancements for human senses. A room built as a whispering gallery will allow a person in a particular location to hear the faintest sounds at other specific places (like doorways). It's not strictly a pneumo-punk device, but it lets a single person react to sounds in multiple locations over a wide area.
The non-human alternative would be a resonant chamber with a diaphragm connected to a mechanical release -- like a trigger sear. A loud enough sound at the correct pitch will apply enough force on the diaphragm to release the sear -- and trigger whatever you like.
Motion detectors might be things like a suspended floor -- the slightest movement by someone standing on the floor will move the floor and trigger a mechanism. Trip wires also work to detect passing past a particular point, and a wire can be made fine enough that, in poor light, it's almost impossible to see.
Proximity detectors might work similarly to cat whiskers -- fine hair-like rods (bamboo can be shaved to make something like this), holding threads taut, will release tension on one or more threads with the slightest touch, and the release of tension can actuate a mechanical trigger, once again.
Chemical detectors are the most difficult to remove the human factor, and how they'd work depends very strongly on the kind of chemical you need to detect. Flammable gases are the original reason for a Davy lamp -- an open flame inside a fine metal mesh, which prevents ignition from passing the mesh, but will glow with a blue lambence when a flammable mixture is present. Similar devices might detect lack of oxygen (flame gutters or extinguishes). Otherwise it's mainly something that will alert a watchful human, once again -- a piece of blotter paper soaked in a solution to change color when exposed to a particular gas, for instance.