A digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410) comprising an inner structure, a skin (610, 6210, 6310, 6410, 7120), and a housing covering said inner structure wherein: the inner structure holds an electric circuit and a first acoustic transmitter (100, 930) together, said first acoustic transmitter (100, 930) being detached from said electric circuit and configured to transmit acoustic signals; and the skin (610, 6210, 6310, 6410, 7120) being removable; the digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410) further comprising: a resilient holder (120,250) comprising: a base longitudinally extended along said pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); and extensions rising perpendicularly from either side of said base to secure said resilient holder (120, 250) to a body of said digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); wherein a U shaped cross section of the resilient holder is configured for confinement of a part of said electric circuit within said pen housing; wherein said resilient holder (120, 250) is configured to mechanically press said electric circuit into electrical connection with said first acoustic transmitter (100, 930) upon application of mechanical pressure applied on said resilient holder (120, 250) from said housing; wherein said resilient holder (120, 250) has elasticity to enable easy assembly by sliding the resilient holder (120, 250) into position. the inner structure holds an electric circuit and a first acoustic transmitter (100, 930) together, said first acoustic transmitter (100, 930) being detached from said electric circuit and configured to transmit acoustic signals; and the skin (610, 6210, 6310, 6410, 7120) being removable; the digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410) further comprising: a resilient holder (120,250) comprising: a base longitudinally extended along said pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); and extensions rising perpendicularly from either side of said base to secure said resilient holder (120, 250) to a body of said digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); a resilient holder (120,250) comprising: a base longitudinally extended along said pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); and extensions rising perpendicularly from either side of said base to secure said resilient holder (120, 250) to a body of said digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); a base longitudinally extended along said pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); and extensions rising perpendicularly from either side of said base to secure said resilient holder (120, 250) to a body of said digital pen (1000, 6100, 6200, 6300, 6400, 700, 800, 1410); wherein a U shaped cross section of the resilient holder is configured for confinement of a part of said electric circuit within said pen housing; wherein said resilient holder (120, 250) is configured to mechanically press said electric circuit into electrical connection with said first acoustic transmitter (100, 930) upon application of mechanical pressure applied on said resilient holder (120, 250) from said housing; wherein said resilient holder (120, 250) has elasticity to enable easy assembly by sliding the resilient holder (120, 250) into position.