This specification is set out in one very small part of the 1968 Vienna Convention on Road Traffic , which is mostly concerned to ensure that motor traffic can cross borders without undue problems. Our bit is Article 44. To save you looking it up, a pedal cycle has to have:
- An efficient brake
- A bell – and no other audible warning device
- A red rear reflector
- Red rear lamp
- White or selective yellow front lamp
If the country you're visiting doesn't require all of those things on its own bikes of course, you don't need them either. As a visitor, you have the option of pick and mix between the traffic law of that country and the above requirements for international use of a pedal cycle.
Some parts of the International specification are lower than British regulations , but others are more onerous, so if your bike is legal to use Britain, it doesn't follow that it's legal everywhere else.
There will be no problem with brakes, since here we sensibly require two, but bells and lamps may seem an imposition when visiting countries that require such things.
Quite a lot of countries do require bells - even some other parts of the UK - whereas in Britain we merely require that the bike is sold with  one. Wheel your bike off a ferry into Holland or Northern Ireland however, and you may wish you'd left that bell on the handlebars!
Travellers who plan to ride in the dark will surely take lights, but most people holiday in summer when the days are long and don't expect to need any. That's fine in most countries, but Germany requires lamps on most sorts of bikes 24/7 (just fitted, not switched on unless it's dark), so if you're going there, you'd better have some. Fortunately the International Convention goes no further than to define the colour of light. So this won't have to be the dynamo system specified by German traffic law: token battery lamps will do.
Bearing all this in mind, it's best to have a bell (but not a horn) already fitted, plus a rear reflector, and to carry a couple of lamps whenever you travel.
Visitors to Britain
Provided your bike has at least one brake already (fixed wheel does not count as a brake internationally), its welcome to Britain! Lights and a red rear reflector will be needed only if you ride it in the dark . And although you will find a bell useful, given that most of our cycletracks are shared with pedestrians, it's not a legal necessity unless you visit such outlying parts of UK as Northern Ireland and the Isle of Man.