Alarm is a really good idea, the problem is when I had one I was plagued by false alarms in windy conditions. Now this may sound naff but it actually works a treat, I bought a personal attack alarm pictured below for £4 of fleabay, I have a piece of monofilament line one end attached via a small clip to the bike the other to the alarm, alarm is hidden discretely nearby, someone moves the bike and it pulls the pin sending out 143Db siren, you can be as poetic as room permits when it comes to hiding the siren, I don't get any false alarms and because the monofilament is so thin it can't be seen unless you really look hard, especially at night when the majority of thieving scum go about their business.s-l1600.jpg The one i have talks and warns you the bike as an alarm then bleeps a few times, if it is moved again within a few seconds the alarm goes off and by heck it makes a racket 120db's worth