Métro & Trains, Paris
Be careful if you're female on the metro no matter what time of day. Guys like to 'rub up' against girls of all ages and make sure you're always holding onto your valuables. I almost got robbed twice in broad daylight. One time two guys got on either side and started feeling my back pocket. I was very lucky that i had just moved my wallet to my front pocket. I realized what was happening and went nuts on these two Algerians. Another time, I was walking through a turnstyle and I felt someone touching my backpack. I turned around and this guy already had his hand in there. Again, I went nuts on him and pushed him down and ran. Of course, there's no gendarmerie when you need them most.
Some of the metro underground stops can be quite scary if you are getting off during the evening. I would suggest that if you are a woman travelling alone, that you try to get off at a busier stop. These tunnels can be quite long and winding and during the evenings, there are panhandlers who can get quite agressive.
Also, use caution when you are in crowded places--particularly Saturday markets. Pickpocketers love to work these markets and I would recommend keeping your money in several places on your person.
Travelling by metro is always essential but watch out for pickpockets in the stations. Pickpockets know which stations are frequented by tourists so always watch out for your valuables. Pickpockets are usually innocent looking children or young adults.
I think Paris is quiet a safe place, but still just be careful when you walk alone at night or go to Metro station especially if you are a woman.
One more thing is the 'STRIKE', it happened quiet many times when I was there and I could not visit some places :-(
TAKE YOUR METRO MAP ALL THE TIME, make sure which station you must go and in which area you are at.
Do not let go of any tickets you buy!! You see the ticket to the left? That was my ticket to the top of the Eiffel Tower....notice how it looks so unused? I put it down for a second to put my change away, and my tour leader picked it up thinking one of us had lost it. Well, he didn't ask me if it was mine, so I ended up spending an hour or so alone under the Tower talking with creepy yet charming men who wanted to take my picture...I later got it back from my teacher, but it still sucked.
And PS: the ticket counter ladies do not care if you lost it...back of the queue!
These warnings are mostly for women:
Avoid distant parks and areas at night. Also the last metros and RER:s are not the best place to be. I once tried to avoid the last metro by partying late, and taking the first metro, BUT there was something I wouldn't have wanted to see... just be careful!!
The Paris Metro ( subway ) is fairly safe. Keep an eye on your valubles as in most big cities. Again, check with a guide book where to avoid. Only a few places are risky. Most of the main tourist areas are safe.
At night, the metro is typically safe, but try to avoid the stops that have long, extended hallways between platforms where unpleasant folks can easily relieve you of your goodies in relative seclusion. This includes: Chatelet les Halles, Chateau Rouge, Gare de Nord, Strasbourg-St. Denis, Reaumur-Sebastopol and Montparnasse-Bienvenue.
If you go out at night in Paris by metro or train, check when the stations close; the metro generally closes around 2 a.m and opens again about 6.30 am... and if you miss the last train...you're not allowed to sleep in the metro ;)
Be careful going on the metro late at night - there are quite a lot of not so well lit walkways and some lines are less safe than others.
I have also heard of a lot of cases of people being mugged in Paris but I guess this is like any big city - just be careful where you wander off to.
beware if you are the type who like to avoid paying on the Metro. The last two occasions we have visited Paris, both times only for a couple of days, we have been pounced by the 'inspection squad'. Lucky for us we had our tickets, but we've never been pounced anywhere else!
The usual safety precautions would suffice. If you're taking the Paris Metro, take extra care of your belongings. My ex-colleague had her handbag stolen in the subway because the snatch thieves thought she was some rich Japanese tourist. Not! For my girlfriends and I, we didn't encounter any unpleasant incidents. We were extremely careful and alert of our surroundings. :-)
Make sure you are too.
It might actually take some time to walk from the Metro station entrance to the train. The tunnels are sometimes fairly long and it might not be a good idea to walk alone at night. Having some company is always a good idea.
If you're leaving Paris by train, or passing through, make sure you go to the correct train station! Many tourists don't realize that Paris has 5 train stations and that you often have to travel from one to the other by metro. Don't assume that your connecting train is leaving from the same station because they usually don't!
Be prepared for sudden and unexplained termination of underground operation. I don't know if it was a unique situation but suddenly the train stopped. Passengers were hearded onto busses and to final destination. There was no announcement of why or where we were at any time. It was a bit frightening to be transported with no orientation as to where we were or when we should get off the bus to be at our particular destination.