Current ambient ionization sources for mass spectrometry (MS) are typically connected to gas cylinders, high-voltage supply, injection pump, and other accessory equipment, which hinder the popularization of MS in the field of on-site detection. Here, we developed a wireless pocket-size "MasSpec Pointer" (weights 65 g) based on arc discharge powered by a 3.7 V polymer Li battery for ambient ionization MS. A high voltage of 5600 V and 20 kHz was generated from the boost coil to penetrate air and form a plasma. The relative standard deviation (RSD) of the high-voltage pulses is 3.8%, leading to a stable discharge and a good quantification performance. A mini diaphragm pump was used to cool the plasma from ∼600 to ∼40 °C and to blow the plasma into a jet, which facilitates sampling. MasSpec Pointer can work well at both positive- and negative-ion modes without any modification and can quickly test gaseous, liquid, or solid samples. The limit of detection of this device for atrazine (an agrochemical) is lower than 0.1 ng/mL. MasSpec Pointer has shown its ability to pinpoint the double-bond location of fatty acid isomers without derivatization reagents or light illumination. Agrochemicals from the surface of an apple and daily chemicals from the surface of a finger were detected successfully using MasSpec Pointer coupled with a miniature mass spectrometer. We believe the "point-and-shoot" device coupled with mini-MS brings the hope for an age of detecting chemicals on-site by nonprofessionals.