The Morse code signal of the spark transmitter consisted of pulses of radio waves called damped waves which repeated at an audio rate, so they were audible as a buzz or tone in a receiver's earphones.
It consisted of a vibrating switch contact between the receiver's detector and earphone, which was repeatedly opened by an electromagnet.
It functioned as a crude modulator; it interrupted the signal from the detector at an audio rate, producing a buzz in the earphone whenever the carrier was present.
Around 1915 the tikker was replaced by a better means of accomplishing the same thing; the heterodyne receiver invented by Reginald Fessenden in 1902.
After vacuum tube oscillators were invented in 1913 by Alexander Meissner the heterodyne receiver replaced the tikker.