Realistically your are governed by the size of two components - the battery and the gsm modem. Simplest way is Uno, GSM Shield, tilt switch (I'm assuming a mercury type tilt switch in the absence of information) and battery.
Realistically your are governed by the size of two components - the battery and the gsm modem. Simplest way is Uno, GSM Shield, tilt switch (I'm assuming a mercury type tilt switch in the absence of information) and battery.