Hitting things together can provide some kind of sound signal. Rock on rock, wood on wood, metal on metal. Hitting something hollow better than something solid, but "needs must."

What about hitting your cooking pot or kettle with a spoon, stick or whatever else is handy?

Hold or hang by the handle; don't grip it tightly at the rim because that will tend to deaden the sound. Try hitting it in different places on the bottom and sides to find the "sweet spot" (where an object is most resonant).

A metal water-bottle should work too. I'd guess that stainless steel would give off more sound than aluminum, but I haven't tested this.

Some pot lids make lots of noise. Again, hold or hang it by its handle and experiment to find the sweet spot.