Is it legal to use counterfeit money as defense against burglars and robbers? I have produced small amounts of counterfeit money, I keep this in a few wallets in a few rooms in my house. When going outside I always have one such wallet with me in case I get robbed. Is using counterfeit money for this specific purpose legal?
Since you don't say which country you're in, it's likely that you're interested in United States law. You are probably in the clear here, though you're getting close enough to the edge of breaking the law that I wouldn't be confident about not being prosecuted and/or convicted. The relevant laws in this case appear to be 18 USC 471, 18 USC 472, and perhaps 18 USC 514. All three of them begin "Whoever, with the intent to defraud...". It's questionable whether creating counterfeit money as a burglar decoy counts as defrauding the burglar.
The issues you describe have existed with signatures from the beginning of their use. There exists a tradeoff between ease of use and reliability, both of forgery and of people falsely claiming forgery. Originally, the closest thing to a signature was the use of seals and signet rings. While relatively hard to forge, it only showed that the possessor of the object agreed. Signatures, especially in cursive font, were developed later. They were in some ways easier to forge(you didn't need to get access to a physical device), but more difficult in others(the seal symbols tended to be used on everything and various improvements in technology had been made), and harder to falsely claim forgery(because most people can't alter their handwriting well). You were affixing your name to the document, indicating that you agreed. Often, the signatures were required to backed up with the signatures of other people as witnesses. They didn't have to agree to the document, they just had to agree to testify that you signed of your own free will. Because witnesses, especially trustworthy and independent witnesses, are hard to come by, some places have dropped that requirement, such as checks and signing a aper receipt when using a credit card. But for some important documents, certain jurisdictions still require witnesses, including large transactions (a document relating to a car insurance payout I recently had required a witness to confirm my signature) and marriages. However, with electronic media, the point of a signature is more to indicate deliberate acceptance of terms, with verification of an individual being left to other processes (e.g. IP address, MAC address, linkage to a specific email account, etc.), so forgery is less of an issue. I have also seen "signatures" amount to checkboxes and "I agree" buttons. Generally, the higher the stakes and "more legal" the agreement, the more likely to these have been the "typed signatures" that you describe, but this seems to be decreasing in frequency, suggesting that its purpose was to stop gap a hole in legal acceptance by judges/courts/laws with regards to electronic communications. Addendum: It should also note that the replacement of seals by signatures is not universal; for instance in Japan, seals are still used over signatures in the majority of cases.
Is this legal? Generally yes, unless it unlawfully exceeds the scope of the license. Also, if it is, how can I check if it's permitted by the original store's EULA? Read the whole EULA, focusing on terms related to resale, assignment, and transferability.
“Never” is a very big word… If a burglar stabs someone in claimed self defense, then we have evidence that this was an armed burglary, so that won’t go down well for that burglar. And your rights to self defence are greatly diminished if you caused that situation illegally. So should you get into the situation, try to run away if at all possible. If you had any chance at all to escape your self defence argument will not be accepted. The only possible situation with self defence is if you are threatened with illegal violence that cannot be justified by the fact that you are a criminal. For example you enter a home, two people with guns inside catch you, bind you to a chair so you are no danger at all, and instead of calling the police they announce they will kill or maim you. This is of course very unlikely to happen.
This is known as a retroactive or ex post facto law. Such laws are explicitly forbidden by the US Constitution (Wikipedia reference), and are generally frowned on in jurisdictions where the rule of law applies, partly because it is difficult to prove criminal intent when your action was not at the time criminal.
Here is an excellent (and extensive) explanation of jurisprudence regarding the "good faith exception" to the admissibility of evidence found due to an error. In short: Yes, the contraband found in Unit B would be evidence admissible in court. (Of course, evidence found in Unit B would only support charges against whomever had a nexus to that property. If the owner of Unit C had no access to Unit B, then evidence in Unit B would not per se implicate him in a crime.) Law enforcement will not return seized property if it believes the property is "contraband." As an example, in Pennsylvania a person can petition a court for return of property seized by law enforcement: Rule 588 requires the petitioner to establish entitlement to lawful possession of the property, but the motion will be rejected if the State successfully argues that the property is contraband, or "derivative contraband" (which has been defined in case law to mean there is "a specific nexus between the property and criminal activity").
The Constitution only regulates the powers of the government; it doesn't directly say what the people can and can't do. In particular, it doesn't say directly that nobody except Congress can coin money. However, it does give the government the power to make laws, which are binding on the population. So Congress possibly could make a law forbidding cryptocurrencies, or at least regulating them, under the "regulating the value thereof" clause. However, they haven't done so. In the case of the Liberty Dollar, there are some specific laws that apply. They were convicted of violating 18 USC 485, which forbids the making of physical gold or silver coins that resemble US or foreign money, and 18 USC 486, which forbids creating or passing any physical metal coins as money (as well as other conspiracy charges, aiding and abetting, etc). None of these laws apply to cryptocurrency because they are not physical metal coins. Given that Congress has been explicitly given the power to coin and regulate the value of money in the United States, how are cryptocurrencies, such as Bitcoin, Ethereum, and Basis created, distributed, and redeemed such that they have not been found unconstitutional? The power to regulate includes the power to not regulate. As a slight tangent, what laws allow for the creation and distribution of cryptocurrencies? In a free society, "everything is permitted that is not forbidden". We don't need a law specifically allowing the creation and distribution of cryptocurrencies; it's sufficient that there is no law that forbids it.
As far as I am aware there is no prohibition against bartering firearms in general. This would be an odd prohibition since it is legal to gift and lend firearms. However, some of your situations change this. could I legally manufacture and exchange a firearm If you manufactured a firearm with the intent to sell you would be required to have an FFL. If this was a one-off sale of a firearm you manufactured at some point in the past for personal use this can be legal without an FFL. There are some additional requirements for the transfer. No party is a known criminal It is illegal to sell or give a firearm to someone you know to be a prohibited possessor. Not all criminals are prohibited from owning firearms, but this helps keep you safe. No party inspects the ID of the other or performs a background check This is state dependent. Some states make you go through an FFL for all transfers, others are much less strict. New Hampshire does not require private sales to go through an FFL if you know the buyer personally. Each party is known to be or appears to be old enough to own a firearm legally This is required for your scheme to be legal. One party barters regularly in this manner using firearms and firearm components This person is now engaged in the business of selling firearms and must be a registered FFL and jump through all the corresponding hoops. No party is licensed to sell firearms Not typically required, unless you do this in a regular basis.