A tunable carbon nanotube electromechanical oscillator is reported, demonstrating the ability to tune resonance frequency and detect small forces. The device consists of a doubly clamped carbon nanotube suspended over a trench between two metal electrodes. The nanotube's motion is actuated and detected via electrostatic interaction with a gate electrode. A gate voltage induces a charge on the nanotube, creating an electrostatic force that causes oscillation. The oscillation is detected by the change in conductance of the nanotube, which is modulated by the motion. The nanotube is used as a mixer to detect the conductance change, avoiding capacitive currents between the gate and drain electrodes. The resonance frequency can be tuned by adjusting the DC gate voltage, which controls the tension in the nanotube. The measured resonance frequency shifts with increasing DC gate voltage, and multiple resonances are observed, corresponding to different vibrational modes of the nanotube. Theoretical simulations show that the resonance frequency depends on the gate voltage and the mechanical properties of the nanotube. The frequency dependence of the nanotube oscillations with the DC gate voltage is in good agreement with theoretical predictions. The quality factor Q of the oscillator is important for most applications, and is in the range of 40–200 for the samples studied. The quality factor decreases with increasing pressure in the vacuum chamber, and the resonance is no longer observed above pressures of 10 torr. The sensitivity of the device is limited by Johnson–Nyquist electronic noise, and the smallest detected motion is about 0.5 nm on resonance. The force sensitivity is about 1 fN Hz⁻¹/², which is within a factor of ten of the highest force sensitivities measured at room temperature. The ultimate limit on force sensitivity is set by the thermal vibrations of the nanotube, and the observed sensitivity is 50 times lower than this limit. This is probably due to the relatively low values of transconductance for the measured nanotubes. At low temperatures, the sensitivity should increase by orders of magnitude owing to high transconductance associated with Coulomb oscillations. Even without increasing Q, force sensitivities below 5 aN should theoretically be attainable at low temperatures. This is comparable to the highest sensitivities measured. The combination of high sensitivity, tunability, and high-frequency operation makes nanotube oscillators promising for a variety of scientific and technological applications.A tunable carbon nanotube electromechanical oscillator is reported, demonstrating the ability to tune resonance frequency and detect small forces. The device consists of a doubly clamped carbon nanotube suspended over a trench between two metal electrodes. The nanotube's motion is actuated and detected via electrostatic interaction with a gate electrode. A gate voltage induces a charge on the nanotube, creating an electrostatic force that causes oscillation. The oscillation is detected by the change in conductance of the nanotube, which is modulated by the motion. The nanotube is used as a mixer to detect the conductance change, avoiding capacitive currents between the gate and drain electrodes. The resonance frequency can be tuned by adjusting the DC gate voltage, which controls the tension in the nanotube. The measured resonance frequency shifts with increasing DC gate voltage, and multiple resonances are observed, corresponding to different vibrational modes of the nanotube. Theoretical simulations show that the resonance frequency depends on the gate voltage and the mechanical properties of the nanotube. The frequency dependence of the nanotube oscillations with the DC gate voltage is in good agreement with theoretical predictions. The quality factor Q of the oscillator is important for most applications, and is in the range of 40–200 for the samples studied. The quality factor decreases with increasing pressure in the vacuum chamber, and the resonance is no longer observed above pressures of 10 torr. The sensitivity of the device is limited by Johnson–Nyquist electronic noise, and the smallest detected motion is about 0.5 nm on resonance. The force sensitivity is about 1 fN Hz⁻¹/², which is within a factor of ten of the highest force sensitivities measured at room temperature. The ultimate limit on force sensitivity is set by the thermal vibrations of the nanotube, and the observed sensitivity is 50 times lower than this limit. This is probably due to the relatively low values of transconductance for the measured nanotubes. At low temperatures, the sensitivity should increase by orders of magnitude owing to high transconductance associated with Coulomb oscillations. Even without increasing Q, force sensitivities below 5 aN should theoretically be attainable at low temperatures. This is comparable to the highest sensitivities measured. The combination of high sensitivity, tunability, and high-frequency operation makes nanotube oscillators promising for a variety of scientific and technological applications.