Quantity   Component name
1 × TinyLily Mini TinyCircuits Arduino https://www.tiny-circuits.com/tiny-lily-mini-basic-kit.html
1 × Altoids Smalls tin Clean
3 × Grayhill 39-1, C&K 8631, or similar Subminiature SPST NO pushbutton switch http://www.mouser.com/ProductDetail/Grayhill/39-1
1 × Subminiature SPDT center off toggle switch http://www.jpmsupply.com/SPDT-ON-OFF-ON-SubMiniature-Toggle-Switch-p/70137.htm [You can do without center off .]
1 × 110 mAh LiPo battery https://www.sparkfun.com/products/731
1 × Philmore 335 or 340 Miniature DC Coaxial jack, panel mount http://universal-radio.com/catalog/parts/dcplugs.html
1 × LiPo battery charger with programming resistor changed from 2K to 10K https://www.sparkfun.com/products/10217 with programming resistor changed from 2K to 10K (see Fig. 2-4 in the datasheet for the onboard Microchip MCP73831 Charge Management Controller).
1 × 2N3904 Bipolar transistor
1 × 1K 1/8W or 1/16W resistor
1 × Miniature magnetic transducer 16mm or as required