A radar level gauge for determining a process variable of product in a tank, said gauge comprising: transceiver circuitry configured to obtain a tank signal by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said tank signal including a plurality of peaks representing echoes from the interior of said tank; and processing circuitry configured to: process said tank signal to identify a surface echo, and when a surface echo can be identified, determine said process variable based on said surface echo; when no surface echo can be identified in the tank signal, entering a wait state, said wait state including: a) storing the tank signal in memory, b) obtaining a wait state tank signal, said wait state tank signal obtained by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said wait state tank signal including a plurality of peaks representing echoes from the interior of said tank, c) comparing said wait state tank signal with the stored tank signal to determine a tank signal difference measure, d) repeating steps b) and c) until the tank signal difference measure is greater than a predefined threshold, e) processing said wait state tank signal to identify a surface echo, and f) when no surface echo can be identified in said wait state tank signal, setting an alarm. transceiver circuitry configured to obtain a tank signal by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said tank signal including a plurality of peaks representing echoes from the interior of said tank; and processing circuitry configured to: process said tank signal to identify a surface echo, and when a surface echo can be identified, determine said process variable based on said surface echo; when no surface echo can be identified in the tank signal, entering a wait state, said wait state including: a) storing the tank signal in memory, b) obtaining a wait state tank signal, said wait state tank signal obtained by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said wait state tank signal including a plurality of peaks representing echoes from the interior of said tank, c) comparing said wait state tank signal with the stored tank signal to determine a tank signal difference measure, d) repeating steps b) and c) until the tank signal difference measure is greater than a predefined threshold, e) processing said wait state tank signal to identify a surface echo, and f) when no surface echo can be identified in said wait state tank signal, setting an alarm. process said tank signal to identify a surface echo, and when a surface echo can be identified, determine said process variable based on said surface echo; when no surface echo can be identified in the tank signal, entering a wait state, said wait state including: a) storing the tank signal in memory, b) obtaining a wait state tank signal, said wait state tank signal obtained by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said wait state tank signal including a plurality of peaks representing echoes from the interior of said tank, c) comparing said wait state tank signal with the stored tank signal to determine a tank signal difference measure, d) repeating steps b) and c) until the tank signal difference measure is greater than a predefined threshold, e) processing said wait state tank signal to identify a surface echo, and f) when no surface echo can be identified in said wait state tank signal, setting an alarm. a) storing the tank signal in memory, b) obtaining a wait state tank signal, said wait state tank signal obtained by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said wait state tank signal including a plurality of peaks representing echoes from the interior of said tank, c) comparing said wait state tank signal with the stored tank signal to determine a tank signal difference measure, d) repeating steps b) and c) until the tank signal difference measure is greater than a predefined threshold, e) processing said wait state tank signal to identify a surface echo, and f) when no surface echo can be identified in said wait state tank signal, setting an alarm.