A syringe (10; 30; 40), comprising: a plunger having a shaft extending longitudinally between a proximal end and a distal end, the shaft including a first section and a second section; a barrel having a proximal end and a distal end and a cylindrical sidewall extending longitudinally between the proximal and distal ends, the sidewall defining an internal volume, the distal end of the plunger being inserted into a proximal end of the barrel and being movable within the internal volume with respect to the barrel in the longitudinal direction; a first probe and a second probe; and a microcontroller disposed on the barrel and in electrical communication with the first and second probes (15A, 15B), the microcontroller being configured to: (i) measure a capacitance between the first and second probes (15A, 15B), the measured capacitance having a first capacitance value when the first section of the plunger shaft is between the first and second probes (15A, 15B) and a second capacitance value different from the first capacitance value when the second section of the plunger shaft is between the first and second probes (15A, 15B), and (ii) determine that an injection has been completed when the second capacitance value is measured, the syringe (10; 30; 40) being characterized in that the first section of the shaft has a first diameter, the second section of the shaft has a second diameter different from the first diameter, the second section being disposed between the first section and the proximal end of the plunger, and the first and second probe (15A, 15B) are disposed on the barrel adjacent a proximal end of the barrel, the first and second probes (15A, 15B) being opposite to one another such that the interior volume of the barrel is radially between the first and second probes (15A, 15B). a plunger having a shaft extending longitudinally between a proximal end and a distal end, the shaft including a first section and a second section; a barrel having a proximal end and a distal end and a cylindrical sidewall extending longitudinally between the proximal and distal ends, the sidewall defining an internal volume, the distal end of the plunger being inserted into a proximal end of the barrel and being movable within the internal volume with respect to the barrel in the longitudinal direction; a first probe and a second probe; and a microcontroller disposed on the barrel and in electrical communication with the first and second probes (15A, 15B), the microcontroller being configured to: (i) measure a capacitance between the first and second probes (15A, 15B), the measured capacitance having a first capacitance value when the first section of the plunger shaft is between the first and second probes (15A, 15B) and a second capacitance value different from the first capacitance value when the second section of the plunger shaft is between the first and second probes (15A, 15B), and (ii) determine that an injection has been completed when the second capacitance value is measured, (i) measure a capacitance between the first and second probes (15A, 15B), the measured capacitance having a first capacitance value when the first section of the plunger shaft is between the first and second probes (15A, 15B) and a second capacitance value different from the first capacitance value when the second section of the plunger shaft is between the first and second probes (15A, 15B), and (ii) determine that an injection has been completed when the second capacitance value is measured, the syringe (10; 30; 40) being characterized in that the first section of the shaft has a first diameter, the second section of the shaft has a second diameter different from the first diameter, the second section being disposed between the first section and the proximal end of the plunger, and the first and second probe (15A, 15B) are disposed on the barrel adjacent a proximal end of the barrel, the first and second probes (15A, 15B) being opposite to one another such that the interior volume of the barrel is radially between the first and second probes (15A, 15B).