I have this tracker fitted to of all my trials bikes after my Montesa repsol was stolen in 2012 costing me £5k
See eBay number 111580231763 it emails if the bike moves then you can follow it's location on any smart phone or computer it's £85 plus £11 per month.
or see https://biketrac.co.uk/ this is £299 and £10 a month much better system as soon as it moves they call you.
The device is the size of a matchbox and just needs a battery change every 12 months there are no advertising stickers to say it's got a tracker otherwise thieves would chop it up for parts.
Also got to be stored in the house and chained up.
Plus see http://www.msminsurance.co.uk/