My guess would be a screw-jack. They have lots of spare wheels on that car so they would need a jack to help them change wheels :)
Might be, but they're more usually seen standing on their base on the running board or whatever - restraining the jack in that position to stop it falling off the vehicle would be quite difficult to start with & I know from bitter experience that they don't like lying on their sides, as the oil inside can quite easily drain out...
The Osprey New Vanguard 189 'The Rolls-Royce Armoured Car' by David Fletcher has an illustration on page 9 of a RR of the RNAS, during 1915, fitted with klaxon:
Also the profile publication 'Armoured Fighting Vehicles of the World' Volume One, Chapter 1 'Early Armoured Cars' by Maj-Gen Duncan has an illustration on page 10 of a RNAS Lanchester armoured car of 1915 fitted with a klaxon:
These are 'high-end' motoring klaxon warning horns. Those interested in aircraft use, my article in Cross & Cockade International of Summer 2017 has details of this:
