Apparently Tchaikovsky meant for actual cannons to be used in the overture, which premiered at Christ the Savior Cathedral in Moscow.
How can you fire cannons (even blanks) inside a church without shattering the windows and deafening your patrons?
FWIW, the Wikipedia page on the overture showed the symphony being performed in the Melbourne Opera House, which I assume is also indoors and has windows.
I imagine you can just lower the amount of explosive used in the blanks until you get something appropriate for the venue.
In the States, its a staple at July 4th concerts, and they usually (or at least, generalizing from the times I’ve seen it) have National Guard units man the cannons. I imagine over the years the various National Guards have gotten it down to a science.
According to the liner notes on a recording I have he wanted the premier to be outside with real cannon, but had to settle for in the cathedral with someone whacking a bass drum subbing for the cannon.
Sometime the concert is indoors, but the cannons are outside… getting relayed direction from the conductor’s assistants. They will be heard inside, trust me 
Modern performances sometimes involve shooting a shotgun into a barrel.
Cannons can be very very small and still make the required “boom” noise. Heck, our high school orchestra performed it indoors using PVC cannons built by our chemistry teacher.
I’m told by my orchestral musician friends that the real problem is not hearing the canon inside but getting the timing down. There is a certain “lock time” on these things, even the 75 mm and 105 mm salute guns. It’s even worse if the attempt is with a friction primer or a slow match to lose gun powder with a real 19th Century muzzle loader. Big drums and shotguns fired into a 55 gal barrel, not so much.
I’ve seen plenty of performances with tympani.
It’s become a staple in outdoor July 4th concerts, in which the cannons are replaced by fireworks . . . also presenting a timing challenge.
I just saw an indoor performance last fall by a professional orchestra, and as far as I could tell they simply played a recording. The orchestra was pretty good, but the recorded cannons sounded way cheesy.
I have heard it performed by a recorder quartet and a toy gun.
Not that this is terribly relevant, but a couple of years ago my community orchestra performed this piece in a very small concert hall, and we had guys from the local science museum set up and explode helium balloons in place of the cannons. Great music and fireballs, what more could you ask for? 
I’m guessing you meant hydrogen.
No, see, it was really innovative and super-sciencey because…
… yeah, you’re right
I remember seeing it performed indoors using a compressed air ‘cannon’. I assumed it was a standard practice for some reason. It was loud and cannon like. I cannot find any hits on google so it must have been specially made device.
From the liner notes of the famous Telarc 1812 recording:
Nice user name / post. Was hoping the last two words were going to be ‘the audience’
I thought Tchaikovsky’s score called for cannons and fireworks.
My most memorable classical concert was a free outdoor one held by the Winnipeg Symphony Orchestra for a milestone birthday. They concluded (well, penultimately, last piece was “Happy Birthday”) with the 1812 Overture with real cannons (courtesy the Canadian Armed Forces), real churchbells (courtesy St. Boniface Basilica just across the river) and real fireworks (which is why it was at the end, waiting until dusk). I distinctly remember all three pieces being present.
Indoors I’ve heard bass drums being used for the cannons, but it’s not nearly as good, and I don’t know anyone who prefers them to the cannons.
Weren’t we all.