Yes, you can place a smoke detector on the wall. However, check the instruction before you do this. Most smoke detectors are suitable for wall-mount and ceiling-mount. But, some don't come with the same qualities. So, read the instruction first. If you place a smoke alarm on the wall, remember to mount it higher. Otherwise, you might end up damaging the smoke detector accidentally. Or your kids might reach it. Quick Tip: Wall mounting a smoke detector in a kitchen is not a good idea. The alarm might go off accidentally due to steam or other reason.