Device for detecting deposition layers in a conduit conducting a liquid or a soft medium and/or for level detection, comprising - a transmitter for generating acoustic waves (SSAW, AWM); - a receiver for receiving acoustic waves (SSAW, AWM) evoked by the transmitter; - a holder carrying the transmitter and the receiver, wherein the holder is configured to be detachably connected to the conduit in such a way that the transmitter and the receiver are arranged on an outer side of a sidewall of the conduit, wherein - a single transmitter-receiver unit provides both the transmitter and the receiver or the transmitter and the receiver are separate units arranged in a distance from one another at the holder in such a way that the transmitter and the receiver are located in a common plane extending at least essentially perpendicular to a longitudinal axis of the conduit when the holder is connected to the conduit; and - an evaluation unit for evaluating signals generated by the receiver upon receipt of acoustic waves (SSAW, AWM) evoked by the transmitter to detect a deposition layer on an inner surface of the sidewall of the conduit and/or for detecting whether the level of the medium is below a predetermined value, wherein the transmitter is configured for evoking Lamb waves or Lamb-Rayleigh waves in the sidewall of the conduit, wherein a portion of the Lamb waves or Lamb-Rayleigh waves is converted into volume acoustic waves in the medium, wherein the receiver is configured for receiving first acoustic waves in the form of the Lamb waves or Lamb-Rayleigh waves excited by the transmitter in the sidewall of the conduit and propagating in the sidewall from the transmitter to the receiver and for receiving second acoustic waves evoked by the transmitter and propagating at least partially through the medium, wherein the second acoustic waves comprise the volume acoustic waves in the medium generated by the conversion of the Lamb waves or Lamb-Rayleigh waves, wherein the evaluation unit is configured to detect a deposition layer on the inner surface of the sidewall of the conduit and/or whether the level of the medium is below a predetermined value by evaluating first signals generated by the receiver upon receipt of the first acoustic waves and second signals generated by the receiver upon receipt of the second acoustic waves. - a transmitter for generating acoustic waves (SSAW, AWM); - a receiver for receiving acoustic waves (SSAW, AWM) evoked by the transmitter; - a holder carrying the transmitter and the receiver, wherein the holder is configured to be detachably connected to the conduit in such a way that the transmitter and the receiver are arranged on an outer side of a sidewall of the conduit, wherein - a single transmitter-receiver unit provides both the transmitter and the receiver or the transmitter and the receiver are separate units arranged in a distance from one another at the holder in such a way that the transmitter and the receiver are located in a common plane extending at least essentially perpendicular to a longitudinal axis of the conduit when the holder is connected to the conduit; and - an evaluation unit for evaluating signals generated by the receiver upon receipt of acoustic waves (SSAW, AWM) evoked by the transmitter to detect a deposition layer on an inner surface of the sidewall of the conduit and/or for detecting whether the level of the medium is below a predetermined value, wherein the transmitter is configured for evoking Lamb waves or Lamb-Rayleigh waves in the sidewall of the conduit, wherein a portion of the Lamb waves or Lamb-Rayleigh waves is converted into volume acoustic waves in the medium, wherein the receiver is configured for receiving first acoustic waves in the form of the Lamb waves or Lamb-Rayleigh waves excited by the transmitter in the sidewall of the conduit and propagating in the sidewall from the transmitter to the receiver and for receiving second acoustic waves evoked by the transmitter and propagating at least partially through the medium, wherein the second acoustic waves comprise the volume acoustic waves in the medium generated by the conversion of the Lamb waves or Lamb-Rayleigh waves, wherein the evaluation unit is configured to detect a deposition layer on the inner surface of the sidewall of the conduit and/or whether the level of the medium is below a predetermined value by evaluating first signals generated by the receiver upon receipt of the first acoustic waves and second signals generated by the receiver upon receipt of the second acoustic waves.