Bike-Alarm for a beginner doable ?

Projects General Guidance
1

Hi...

as a first projekt with use for me, i want to build an Bike-Alarm for my Bike...

BUT: it should be hidden in the sattlepost !

so: there the inner diameter of the Sattle post ist about 22mm

a Arduino Nano fits inside it

what i want:
i want to aktivate the Alarm by a hidden switch

when i leave the Bike, it should aktivate a loud sound, wenn the bike is touched, moved..
so i think a g-sensor (?) would be useful?

how sensitiv the alarm reacts, how fast, how long etc. should be done by the arduino-nano

for the sound i wana use a piezo-speaker
The Arduino should get the power from two LiMn-cells, 7,4V, 1600mah
which are also placed inside the seat-post

is that doable ? from the wiring, the space inside a seat-post (the seatpost is 22mm diameter inside and 300mm long --> 140mm are used by the batteries)
it would be my first project after some "let LED 1 blink and LED 2 go off" - mini-Projekts to see the absolut basics for programming the arduino

2

for the sound i wana use a piezo-speaker

To make enough noise to attract attention/thwart a thief? I don't think so.

Other than that, the project looks doable.

3

i have a bikealarm like this one: Bike Alarm Demo - YouTube (at min. 2 you can hear the alarm)
there is a piezo-speaker (i think it is a piezo speaker ?)
inside

its loud enough and scares thiefs away...

BUT: i don´t like the Code-Thingy..
iam a Bike messanger, and using the code 20 times a day to unlock the bike is too time-consuming
i want a simple hidden switch

also sometimes you make a mistake when tipping the code and the alarm starts, which is very anoing, when all people look at you and your bike

how small can a G-sensor (or are other sensors here more suitable -- for example angle ?) be ?
can it be mounted inside a 22mm-pipe

4

I don't think a piezo buzzer is loud enough. You can use a tansistor or relay to drive an off the shelf noise maker (like a loud bike horn) that is driven with an external battery.

To know how to use a transistor with arduino at http://www.danielsoltis.com/notdatasheets/BC547.pdf

As for the sensor may be you can use a tilt switch positioned at an angle or something else. I am a noob too. Correct me if I made any mistakes.

5

If you're a bike messenger and presumably your bike is particularly precious to you (you can't do your job if it is lost) wouldn't you be better off with something that physically secured the bike rather than just a noise maker?

6

IMHO these alarms are worse than useless. You have to avoid false positives. That is you need to avoid that the alarm goes off when it should not. Then you have to think about what should happen once it goes off. Any sound it will make will usually anoy people but will NOT motivate them for action. In the unlikely case someone would actually bother to look for your bike the thief only needs to say "I have to get rid of this alarm, this is the third time today that it triggers although I disarmed it..."