A new device for continuous measurement of fruit or stem growth on the basis of an optoelectronic reflex sensor and a microcontroller board was developed and successfully tested under open field conditions. The principle of the system is based on the detection of alternating narrow white and blacks bars printed on a flexible tape, which is tightened as a loop around the measured object and slides under an infrared reflex sensor in response to the object's radial growth. The design of this new sensor allows continuous, long term measurements without the need of periodic maintenance or physical adjustments of the measurement device. The new system measures changes of fruit or stem perimeter rather than diameter, thus yielding a more relevant information about the growth of objects which are intrinsically not of perfectly circular cross-sectional shape. The described sensor is very lightweight and does not require any mechanical frame or support structure. The tested prototypes had a measurement resolution of 0.5 mm of perimeter, corresponding to a resolution of about 0.16 mm of diameter for a spherical object. The cost of the sensor is very modest, as it consists of only few and inexpensive components. (C) 2016 Elsevier B.V. All rights reserved.